[13.0] GitLab Runner features to deprecate and remove
This issue keep tracks of deprecation and removal for %"13.0".
For each deprecated part that we plan to remove in %13.0, we should:
1. Create a deprecation issue, with milestone set to %13.0 and epic set to &2254.
1. Add a comment to a deprecated code part:
```golang
// TODO: Remove in 13.0
```
1. Add a deprecation message **before %13.0** in Runner's Changelog.
1. Add a deprecation message **before %13.0** in release blog post.
1. Add the deprecated change with links to related issues and MRs in the list bellow.
At %"13.0" release we should go through the whole list and finally remove all deprecated parts of code.
To Do List:
* [x] Update the `Post deprecation message in the 12.8 release blog post:` @DarrenEastman
* [x] Add again all of these to the %"12.8" release blog post. @DarrenEastman
https://gitlab.com/gitlab-com/www-gitlab-com/-/merge_requests/41307
## Deprecations
- [ ] **Support for legacy variables `os.Expand()` behavior** https://gitlab.com/gitlab-org/gitlab-runner/merge_requests/1677
- [ ] Deprecation issue: https://gitlab.com/gitlab-org/gitlab-runner/issues/4915
- [ ] Add deprecation message to the CHANGELOG: TODO
- [ ] Post deprecation message in release blog post: TODO
- [ ] In %13.0 Remove deprecated code: TODO
- [ ] **Allow service alias from config in Docker executor** https://gitlab.com/gitlab-org/gitlab-runner/merge_requests/1673
- [ ] Deprecation issue: https://gitlab.com/gitlab-org/gitlab-runner/issues/4922
- [ ] Add deprecation message to the CHANGELOG: TODO
- [ ] Post deprecation message in release blog post: TODO
- [ ] In %13.0 Remove deprecated code: TODO
- [ ] **Remove CMD from shell executor** https://gitlab.com/gitlab-org/gitlab-runner/issues/4163
- [ ] Deprecation issue: https://gitlab.com/gitlab-org/gitlab-runner/issues/6099
- [ ] Add deprecation message to the CHANGELOG: TODO
- [ ] Post deprecation message in release blog post: TODO
- [ ] In %13.0 Remove deprecated code: TODO
- [ ] **Remove /debug/jobs/list?v=1 endpoint**
- [ ] Deprecation issue: https://gitlab.com/gitlab-org/gitlab-runner/issues/6361
- [ ] Add deprecation message to the CHANGELOG: TODO
- [ ] Post deprecation message in release blog post: TODO
- [ ] In %13.0 Remove deprecated code: TODO
- [ ] **Remove support for --docker-services flag on register command**
- [ ] Deprecation issue: https://gitlab.com/gitlab-org/gitlab-runner/issues/6404
- [ ] Add deprecation message to the CHANGELOG: TODO
- [ ] Post deprecation message in release blog post: TODO
- [ ] In %13.0 Remove deprecated code: TODO
- [ ] **Remove FF_USE_LEGACY_VOLUMES_MOUNTING_ORDER feature flag**
- [ ] Deprecation issue: https://gitlab.com/gitlab-org/gitlab-runner/issues/6581
- [ ] Add deprecation message to the CHANGELOG: TODO
- [ ] Post deprecation message in release blog post: TODO
- [ ] In %13.0 Remove deprecated code: TODO
- [ ] **Remove legacy build directory caching feature flag**
- [ ] Deprecation issue: https://gitlab.com/gitlab-org/gitlab-runner/issues/4180
- [ ] Add deprecation message to the CHANGELOG: TODO
- [ ] Post deprecation message in release blog post: TODO
- [ ] In %13.0 Remove deprecated code: TODO
- [ ] **Remove Windows 1803 support**
- [ ] Deprecation issue: https://gitlab.com/gitlab-org/gitlab-runner/-/issues/6553
- [ ] Add deprecation message to the CHANGELOG: TODO
- [ ] Post deprecation message in release blog post: TODO
- [ ] In %13.0 Remove deprecated code: TODO
- [ ] **Remove fedora/29 packages**
- [ ] Deprecation issue: https://gitlab.com/gitlab-org/gitlab-runner/issues/16158
- [ ] Add deprecation message to the CHANGELOG: TODO
- [ ] Post deprecation message in release blog post: TODO
- [ ] In %13.0 Remove deprecated code: TODO
**Template**
```markdown
- [ ] **Feature to deprecate** https://gitlab.com/gitlab-org/gitlab-runner/merge_requests/XXX
- [ ] Deprecation issue: https://gitlab.com/gitlab-org/gitlab-runner/issues/XXX
- [ ] Add deprecation message to the CHANGELOG: https://gitlab.com/gitlab-org/gitlab-runner/merge_requests/XXX
- [ ] Post deprecation message in release blog post: https://gitlab.com/gitlab-com/www-gitlab-org/merge_requests/XXX
- [ ] In %13.0 Remove deprecated code: https://gitlab.com/gitlab-org/gitlab-runner/merge_requests/XXX
```
** Removal Posts MR's
* https://gitlab.com/gitlab-com/www-gitlab-com/-/merge_requests/49203
* https://gitlab.com/gitlab-com/www-gitlab-com/-/merge_requests/49190
* https://gitlab.com/gitlab-com/www-gitlab-com/-/merge_requests/49179
* https://gitlab.com/gitlab-com/www-gitlab-com/-/merge_requests/49161
* https://gitlab.com/gitlab-com/www-gitlab-com/-/merge_requests/49150
* https://gitlab.com/gitlab-com/www-gitlab-com/-/merge_requests/49034
* https://gitlab.com/gitlab-com/www-gitlab-com/-/merge_requests/49028
* https://gitlab.com/gitlab-com/www-gitlab-com/-/merge_requests/49025
* https://gitlab.com/gitlab-com/www-gitlab-com/-/merge_requests/49023
* https://gitlab.com/gitlab-com/www-gitlab-com/-/merge_requests/49019
epic