Remove `new_design?` guard from `Design#diff_refs`

The app is never in a situation where `#diff_refs` is called on a design
without a version.

Removing this guard makes it unambiguous that the GraphQL `DesignType`
should have non-null `diff_ref`s

https://gitlab.com/gitlab-org/gitlab-ee/issues/12916
122 jobs for 12916-remove-new-design-guard-on-diff_refs in 58 minutes and 43 seconds (queued for 13 seconds)
latest
Status Job ID Name Coverage
  Prepare
passed #272848166
gitlab-org
compile-assets pull-cache

00:09:20

passed #272848169
gitlab-org
retrieve-tests-metadata

00:00:33

passed #272848168
gitlab-org
setup-test-env

00:07:07

 
  Test
passed #272848329
docker gitlab-org
build-qa-image

00:04:51

passed #272848194
allowed to fail
code_quality

00:12:44

passed #272848331
gitlab-org
danger-review

00:02:05

passed #272848292
gitlab-org
db:check-schema-pg

00:02:42

passed #272848290
gitlab-org
db:migrate:reset-pg

00:05:07

passed #272848296
gitlab-org
db:rollback-pg

00:03:18

passed #272848328
gitlab-org
db:rollback-pg-geo

00:02:41

passed #272848197
allowed to fail
dependency_scanning

00:06:44

passed #272848174
gitlab-org
docs lint

00:02:58

passed #272848288
gitlab-org
downtime_check

00:02:18

passed #272848334
gitlab-org
ee-files-location-check

00:03:29

passed #272848335
gitlab-org
ee-specific-lines-check

00:03:24

passed #272848182
gitlab-org docker
gitlab:assets:compile pull-cache

00:20:50

passed #272848298
gitlab-org
gitlab:setup-pg

00:03:39

passed #272848332
gitlab-org
gitlab_git_test

00:00:47

passed #272848185
gitlab-org
jest

00:16:33

passed #272848184
gitlab-org
karma

00:16:49

68.71%
passed #272848336
gitlab-org
lint-ci-gitlab

00:00:36

passed #272848193
gitlab-org
memory-on-boot

00:04:28

passed #272848191
gitlab-org
memory-static

00:03:32

passed #272848293
gitlab-org
migration:path-pg

00:08:22

passed #272848327
gitlab-org
migration:upgrade-pg-ce-to-ee

00:06:08

passed #272848189
gitlab-org
qa-frontend-node:10

00:16:25

passed #272848188
gitlab-org
qa-frontend-node:8

00:20:20

passed #272848190
gitlab-org allowed to fail
qa-frontend-node:latest

00:19:22

passed #272848186
gitlab-org
qa:internal

00:03:06

passed #272848187
gitlab-org
qa:selectors

00:03:20

passed #272848330
allowed to fail manual
review-build-cng

00:28:50

passed #272848318
gitlab-org
rspec geo pg ee 1/3

00:09:59

passed #272848319
gitlab-org
rspec geo pg ee 2/3

00:08:02

passed #272848321
gitlab-org
rspec geo pg ee 3/3

00:08:45

passed #272848323
gitlab-org
rspec geo pg-10 ee 1/3

00:11:22

passed #272848324
gitlab-org
rspec geo pg-10 ee 2/3

00:08:55

passed #272848326
gitlab-org
rspec geo pg-10 ee 3/3

00:10:01

passed #272848228
gitlab-org
rspec integration pg 1/6

00:20:28

passed #272848229
gitlab-org
rspec integration pg 2/6

00:21:53

passed #272848230
gitlab-org
rspec integration pg 3/6

00:21:24

passed #272848231
gitlab-org
rspec integration pg 4/6

00:21:26

passed #272848238
gitlab-org
rspec integration pg 5/6

00:19:29

passed #272848240
gitlab-org
rspec integration pg 6/6

00:22:19

passed #272848308
gitlab-org
rspec integration pg ee 1/3

00:15:48

passed #272848310
gitlab-org
rspec integration pg ee 2/3

00:14:48

passed #272848311
gitlab-org
rspec integration pg ee 3/3

00:17:25

passed #272848241
gitlab-org
rspec system pg 1/24

00:14:20

passed #272848258
gitlab-org
rspec system pg 10/24

00:11:47

passed #272848259
gitlab-org
rspec system pg 11/24

00:14:37

passed #272848260
gitlab-org
rspec system pg 12/24

00:13:32

passed #272848263
gitlab-org
rspec system pg 13/24

00:12:06

passed #272848268
gitlab-org
rspec system pg 14/24

00:14:46

passed #272848270
gitlab-org
rspec system pg 15/24

00:14:03

passed #272848271
gitlab-org
rspec system pg 16/24

00:13:53

passed #272848272
gitlab-org
rspec system pg 17/24

00:13:06

passed #272848274
gitlab-org
rspec system pg 18/24

00:14:21

passed #272848276
gitlab-org
rspec system pg 19/24

00:15:13

passed #272848243
gitlab-org
rspec system pg 2/24

00:13:25

passed #272848278
gitlab-org
rspec system pg 20/24

00:14:05

passed #272848280
gitlab-org
rspec system pg 21/24

00:12:21

passed #272848281
gitlab-org
rspec system pg 22/24

00:15:32

passed #272848283
gitlab-org
rspec system pg 23/24

00:11:48

passed #272848284
gitlab-org
rspec system pg 24/24

00:15:11

passed #272848244
gitlab-org
rspec system pg 3/24

00:18:54

passed #272848246
gitlab-org
rspec system pg 4/24

00:14:18

passed #272848247
gitlab-org
rspec system pg 5/24

00:14:18

passed #272848249
gitlab-org
rspec system pg 6/24

00:11:16

passed #272848252
gitlab-org
rspec system pg 7/24

00:11:44

passed #272848256
gitlab-org
rspec system pg 8/24

00:11:27

passed #272848257
gitlab-org
rspec system pg 9/24

00:14:09

passed #272848312
gitlab-org
rspec system pg ee 1/5

00:18:02

passed #272848313
gitlab-org
rspec system pg ee 2/5

00:15:31

passed #272848314
gitlab-org
rspec system pg ee 3/5

00:16:08

passed #272848315
gitlab-org
rspec system pg ee 4/5

00:18:30

passed #272848317
gitlab-org
rspec system pg ee 5/5

00:16:37

passed #272848198
gitlab-org
rspec unit pg 1/20

00:17:00

passed #272848213
gitlab-org
rspec unit pg 10/20

00:15:17

passed #272848214
gitlab-org
rspec unit pg 11/20

00:19:13

passed #272848215
gitlab-org
rspec unit pg 12/20

00:18:08

passed #272848216
gitlab-org
rspec unit pg 13/20

00:16:44

passed #272848217
gitlab-org
rspec unit pg 14/20

00:15:43

passed #272848219
gitlab-org
rspec unit pg 15/20

00:17:13

passed #272848220
gitlab-org
rspec unit pg 16/20

00:18:09

passed #272848221
gitlab-org
rspec unit pg 17/20

00:18:53

passed #272848224
gitlab-org
rspec unit pg 18/20

00:16:48

passed #272848225
gitlab-org
rspec unit pg 19/20

00:16:26

passed #272848200
gitlab-org
rspec unit pg 2/20

00:16:50

passed #272848227
gitlab-org
rspec unit pg 20/20

00:18:43

passed #272848205
gitlab-org
rspec unit pg 3/20

00:16:25

passed #272848206
gitlab-org
rspec unit pg 4/20

00:14:36

passed #272848208
gitlab-org
rspec unit pg 5/20

00:14:01

passed #272848209
gitlab-org
rspec unit pg 6/20

00:13:44

passed #272848210
gitlab-org
rspec unit pg 7/20

00:17:59

passed #272848211
gitlab-org
rspec unit pg 8/20

00:17:12

passed #272848212
gitlab-org
rspec unit pg 9/20

00:15:02

passed #272848301
gitlab-org
rspec unit pg ee 1/7

00:13:46

passed #272848302
gitlab-org
rspec unit pg ee 2/7

00:11:58

passed #272848303
gitlab-org
rspec unit pg ee 3/7

00:14:24

passed #272848304
gitlab-org
rspec unit pg ee 4/7

00:13:03

passed #272848305
gitlab-org
rspec unit pg ee 5/7

00:13:00

passed #272848306
gitlab-org
rspec unit pg ee 6/7

00:14:05

failed #272848307
gitlab-org
rspec unit pg ee 7/7

00:14:11

passed #272848286
gitlab-org
rspec-fast-spec-helper

00:04:37

passed #272848195
allowed to fail
sast

00:08:24

passed #272848287
gitlab-org
static-analysis

00:33:42

 
  Review
skipped #272848343
allowed to fail manual
package-and-qa
skipped #272848345
gitlab-org allowed to fail
review-deploy
skipped #272848342
gitlab-org allowed to fail manual
review-docs-cleanup
skipped #272848337
gitlab-org allowed to fail manual
review-docs-deploy-manual
skipped #272848373
gitlab-org allowed to fail manual
review-stop
 
  Qa
skipped #272848397
docker gitlab-org allowed to fail
review-performance
skipped #272848387
docker gitlab-org allowed to fail manual
review-qa-all 1/5
skipped #272848389
docker gitlab-org allowed to fail manual
review-qa-all 2/5
skipped #272848391
docker gitlab-org allowed to fail manual
review-qa-all 3/5
skipped #272848395
docker gitlab-org allowed to fail manual
review-qa-all 4/5
skipped #272848396
docker gitlab-org allowed to fail manual
review-qa-all 5/5
skipped #272848384
docker gitlab-org allowed to fail
review-qa-smoke
 
  Post Test
skipped #272848400
gitlab-org
coverage
skipped #272848402
gitlab-org allowed to fail
flaky-examples-check
skipped #272848399
gitlab-org
jsdoc
skipped #272848398
gitlab-org
lint:javascript:report
skipped #272848401
gitlab-org allowed to fail manual
parallel-spec-reports
 
Name Stage Failure
failed
rspec unit pg ee 7/7 Test
rspec_flaky/: found 2 matching files               
rspec_profiling/: found 1 matching files

WARNING: tmp/capybara/: no matching files
tmp/memory_test/: found 2 matching files

Uploading artifacts to coordinator... ok
id=272848307 responseStatus=201 Created token=YxoopxyN
Uploading artifacts...
junit_rspec.xml: found 1 matching files

Uploading artifacts to coordinator... ok
id=272848307 responseStatus=201 Created token=YxoopxyN
ERROR: Job failed: exit code 1