Drop `epic_id` Column From Vulnerabilities

What does this MR do and why?

epic_id is an ignored column (source)

This MR drops the column for step 2 of the 3-MR drop column process

Check for indexes or constraints

Using the command \d+ vulnerabilities on postgres.ai indicates there ARE indexes and constraints

index	fk constraint

migration output

bundle exec rails db:migrate output

~/gitlab-development-kit/gitlab$ bundle exec rails db:migrate 
main: == [advisory_lock_connection] object_id: 182860, pg_backend_pid: 947800
main: == 20231219132423 RemoveEpicIdColumnFromVulnerabilities: migrating ============
main: -- transaction_open?(nil)
main:    -> 0.0000s
main: -- remove_column(:vulnerabilities, :epic_id)
main:    -> 0.0015s
main: == 20231219132423 RemoveEpicIdColumnFromVulnerabilities: migrated (0.0129s) ===

main: == [advisory_lock_connection] object_id: 182860, pg_backend_pid: 947800
ci: == [advisory_lock_connection] object_id: 183100, pg_backend_pid: 947802
ci: == 20231219132423 RemoveEpicIdColumnFromVulnerabilities: migrating ============
ci: -- transaction_open?(nil)
ci:    -> 0.0000s
ci: -- remove_column(:vulnerabilities, :epic_id)
ci:    -> 0.0023s
ci: == 20231219132423 RemoveEpicIdColumnFromVulnerabilities: migrated (0.0187s) ===

ci: == [advisory_lock_connection] object_id: 183100, pg_backend_pid: 947802

bundle exec rails db:rollback:main output

~/gitlab-development-kit/gitlab$ bundle exec rails db:rollback:main
main: == [advisory_lock_connection] object_id: 182580, pg_backend_pid: 950470
main: == 20231219132423 RemoveEpicIdColumnFromVulnerabilities: reverting ============
main: -- column_exists?(:vulnerabilities, :epic_id)
main:    -> 0.0255s
main: -- add_column(:vulnerabilities, :epic_id, :bigint)
main:    -> 0.0011s
main: -- transaction_open?(nil)
main:    -> 0.0000s
main: -- view_exists?(:postgres_partitions)
main:    -> 0.0010s
main: -- index_exists?(:vulnerabilities, :epic_id, {:algorithm=>:concurrently})
main:    -> 0.0114s
main: -- execute("SET statement_timeout TO 0")
main:    -> 0.0003s
main: -- add_index(:vulnerabilities, :epic_id, {:algorithm=>:concurrently})
main:    -> 0.0020s
main: -- execute("RESET statement_timeout")
main:    -> 0.0003s
main: -- index_name(:vulnerabilities, :epic_id)
main:    -> 0.0000s
main: -- transaction_open?(nil)
main:    -> 0.0000s
main: -- transaction_open?(nil)
main:    -> 0.0000s
main: -- execute("ALTER TABLE vulnerabilities ADD CONSTRAINT fk_1d37cddf91 FOREIGN KEY (epic_id) REFERENCES epics (id) ON DELETE SET NULL NOT VALID;")
main:    -> 0.0030s
main: -- execute("ALTER TABLE vulnerabilities VALIDATE CONSTRAINT fk_1d37cddf91;")
main:    -> 0.0060s
main: == 20231219132423 RemoveEpicIdColumnFromVulnerabilities: reverted (0.0908s) ===

main: == [advisory_lock_connection] object_id: 182580, pg_backend_pid: 950470

bundle exec rails db:rollback:ci output

~/gitlab-development-kit/gitlab$ bundle exec rails db:rollback:ci
ci: == [advisory_lock_connection] object_id: 182500, pg_backend_pid: 950946
ci: == 20231219132423 RemoveEpicIdColumnFromVulnerabilities: reverting ============
ci: -- column_exists?(:vulnerabilities, :epic_id)
ci:    -> 0.0184s
ci: -- add_column(:vulnerabilities, :epic_id, :bigint)
ci:    -> 0.0009s
ci: -- transaction_open?(nil)
ci:    -> 0.0000s
ci: -- view_exists?(:postgres_partitions)
ci:    -> 0.0009s
ci: -- index_exists?(:vulnerabilities, :epic_id, {:algorithm=>:concurrently})
ci:    -> 0.0152s
ci: -- execute("SET statement_timeout TO 0")
ci:    -> 0.0006s
ci: -- add_index(:vulnerabilities, :epic_id, {:algorithm=>:concurrently})
ci:    -> 0.0015s
ci: -- execute("RESET statement_timeout")
ci:    -> 0.0004s
ci: -- index_name(:vulnerabilities, :epic_id)
ci:    -> 0.0000s
ci: -- transaction_open?(nil)
ci:    -> 0.0000s
ci: -- transaction_open?(nil)
ci:    -> 0.0000s
ci: -- execute("ALTER TABLE vulnerabilities ADD CONSTRAINT fk_1d37cddf91 FOREIGN KEY (epic_id) REFERENCES epics (id) ON DELETE SET NULL NOT VALID;")
ci:    -> 0.0038s
ci: -- execute("ALTER TABLE vulnerabilities VALIDATE CONSTRAINT fk_1d37cddf91;")
ci:    -> 0.0037s
ci: == 20231219132423 RemoveEpicIdColumnFromVulnerabilities: reverted (0.0951s) ===

ci: == [advisory_lock_connection] object_id: 182500, pg_backend_pid: 950946

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.

Related to #268154 (closed)