Drop unused index on ci_builds

Ref: #271620 (closed)

What does this MR do and why?

Following up !91473 (merged).

This MR drops index_ci_builds_on_queued_at which is no longer being used according to Thanos.

This will be executed as a no-op migration on gitlab.com as we dropped this index with a CR in gitlab-com/gl-infra/production#7435 (closed).

Screenshots or screen recordings

Database

List of relations  
 Schema |             Name             | Type  |  Owner  |   Table   | Size  | Description   
--------+------------------------------+-------+---------+-----------+-------+-------------  
 public | index_ci_builds_on_queued_at | index | joe_292 | ci_builds | 67 GB |   
(1 row)  

Migrations up

➜  gitlab git:(master) ✗ rails db:migrate:ci
ci: == 20220719081542 DropQueuedAtIndexFromCiBuilds: migrating ====================
ci: -- transaction_open?()
ci:    -> 0.0000s
ci: -- indexes(:ci_builds)
ci:    -> 0.0089s
ci: -- execute("SET statement_timeout TO 0")
ci:    -> 0.0001s
ci: -- remove_index(:ci_builds, {:algorithm=>:concurrently, :name=>"index_ci_builds_on_queued_at"})
ci:    -> 0.0020s
ci: -- execute("RESET statement_timeout")
ci:    -> 0.0002s
ci: == 20220719081542 DropQueuedAtIndexFromCiBuilds: migrated (0.0152s) ===========

➜  gitlab git:(master) ✗ rails db:migrate:main
main: == 20220719081542 DropQueuedAtIndexFromCiBuilds: migrating ====================
main: -- transaction_open?()
main:    -> 0.0000s
main: -- indexes(:ci_builds)
main:    -> 0.0087s
main: -- execute("SET statement_timeout TO 0")
main:    -> 0.0002s
main: -- remove_index(:ci_builds, {:algorithm=>:concurrently, :name=>"index_ci_builds_on_queued_at"})
main:    -> 0.0012s
main: -- execute("RESET statement_timeout")
main:    -> 0.0002s
main: == 20220719081542 DropQueuedAtIndexFromCiBuilds: migrated (0.0142s) ===========

Migrations down

➜  gitlab git:(master) ✗ rails db:rollback:ci
ci: == 20220719081542 DropQueuedAtIndexFromCiBuilds: reverting ====================
ci: -- transaction_open?()
ci:    -> 0.0000s
ci: -- index_exists?(:ci_builds, :queued_at, {:name=>"index_ci_builds_on_queued_at", :algorithm=>:concurrently})
ci:    -> 0.0082s
ci: -- execute("SET statement_timeout TO 0")
ci:    -> 0.0002s
ci: -- add_index(:ci_builds, :queued_at, {:name=>"index_ci_builds_on_queued_at", :algorithm=>:concurrently})
ci:    -> 0.0019s
ci: -- execute("RESET statement_timeout")
ci:    -> 0.0002s
ci: == 20220719081542 DropQueuedAtIndexFromCiBuilds: reverted (0.0148s) ===========

➜  gitlab git:(master) ✗ rails db:rollback:main
main: == 20220719081542 DropQueuedAtIndexFromCiBuilds: reverting ====================
main: -- transaction_open?()
main:    -> 0.0000s
main: -- index_exists?(:ci_builds, :queued_at, {:name=>"index_ci_builds_on_queued_at", :algorithm=>:concurrently})
main:    -> 0.0076s
main: -- execute("SET statement_timeout TO 0")
main:    -> 0.0001s
main: -- add_index(:ci_builds, :queued_at, {:name=>"index_ci_builds_on_queued_at", :algorithm=>:concurrently})
main:    -> 0.0017s
main: -- execute("RESET statement_timeout")
main:    -> 0.0001s
main: == 20220719081542 DropQueuedAtIndexFromCiBuilds: reverted (0.0132s) ===========

Impact

Reduced ci_builds size by 70GB

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.