Remove unused issue trigram indexes

What does this MR do and why?

Removes indexes that are no longer needed.

These are already removed for GitLab.com in !103733 (merged)

Migration output

main: == 20221122063922 RemoveIssueTitleTrigramIndex: migrating =====================
main: -- transaction_open?()
main:    -> 0.0000s
main: -- view_exists?(:postgres_partitions)
main:    -> 0.0062s
main: -- indexes(:issues)
main:    -> 0.0082s
main: -- execute("SET statement_timeout TO 0")
main:    -> 0.0001s
main: -- remove_index(:issues, {:algorithm=>:concurrently, :name=>"index_issues_on_title_trigram"})
main:    -> 0.0016s
main: -- execute("RESET statement_timeout")
main:    -> 0.0002s
main: == 20221122063922 RemoveIssueTitleTrigramIndex: migrated (0.0244s) ============

main: == 20221122064537 RemoveIssueDescriptionTrigramIndex: migrating ===============
main: -- transaction_open?()
main:    -> 0.0000s
main: -- view_exists?(:postgres_partitions)
main:    -> 0.0004s
main: -- indexes(:issues)
main:    -> 0.0091s
main: -- remove_index(:issues, {:algorithm=>:concurrently, :name=>"index_issues_on_description_trigram"})
main:    -> 0.0010s
main: == 20221122064537 RemoveIssueDescriptionTrigramIndex: migrated (0.0138s) ======

ci: == 20221122063922 RemoveIssueTitleTrigramIndex: migrating =====================
ci: -- transaction_open?()
ci:    -> 0.0000s
ci: -- view_exists?(:postgres_partitions)
ci:    -> 0.0006s
ci: -- indexes(:issues)
ci:    -> 0.0095s
ci: -- execute("SET statement_timeout TO 0")
ci:    -> 0.0002s
ci: -- remove_index(:issues, {:algorithm=>:concurrently, :name=>"index_issues_on_title_trigram"})
ci:    -> 0.0028s
ci: -- execute("RESET statement_timeout")
ci:    -> 0.0002s
ci: == 20221122063922 RemoveIssueTitleTrigramIndex: migrated (0.0180s) ============

ci: == 20221122064537 RemoveIssueDescriptionTrigramIndex: migrating ===============
ci: -- transaction_open?()
ci:    -> 0.0000s
ci: -- view_exists?(:postgres_partitions)
ci:    -> 0.0004s
ci: -- indexes(:issues)
ci:    -> 0.0072s
ci: -- remove_index(:issues, {:algorithm=>:concurrently, :name=>"index_issues_on_description_trigram"})
ci:    -> 0.0012s
ci: == 20221122064537 RemoveIssueDescriptionTrigramIndex: migrated (0.0117s) ======

main: == 20221122064537 RemoveIssueDescriptionTrigramIndex: reverting ===============
main: -- execute("SET statement_timeout TO 0")
main:    -> 0.0003s
main: -- execute("        CREATE INDEX CONCURRENTLY IF NOT EXISTS index_issues_on_description_trigram ON issues\n          USING gin (description gin_trgm_ops) WITH (fastupdate='false')\n")
main:    -> 0.0125s
main: -- execute("RESET statement_timeout")
main:    -> 0.0002s
main: == 20221122064537 RemoveIssueDescriptionTrigramIndex: reverted (0.0142s) ======

main: == 20221122063922 RemoveIssueTitleTrigramIndex: reverting =====================
main: -- execute("SET statement_timeout TO 0")
main:    -> 0.0003s
main: -- execute("        CREATE INDEX CONCURRENTLY IF NOT EXISTS index_issues_on_title_trigram ON issues\n          USING gin (title gin_trgm_ops) WITH (fastupdate='false')\n")
main:    -> 0.0087s
main: -- execute("RESET statement_timeout")
main:    -> 0.0002s
main: == 20221122063922 RemoveIssueTitleTrigramIndex: reverted (0.0108s) ============

ci: == 20221122064537 RemoveIssueDescriptionTrigramIndex: reverting ===============
ci: -- execute("SET statement_timeout TO 0")
ci:    -> 0.0003s
ci: -- execute("        CREATE INDEX CONCURRENTLY IF NOT EXISTS index_issues_on_description_trigram ON issues\n          USING gin (description gin_trgm_ops) WITH (fastupdate='false')\n")
ci:    -> 0.0094s
ci: -- execute("RESET statement_timeout")
ci:    -> 0.0002s
ci: == 20221122064537 RemoveIssueDescriptionTrigramIndex: reverted (0.0119s) ======

ci: == 20221122063922 RemoveIssueTitleTrigramIndex: reverting =====================
ci: -- execute("SET statement_timeout TO 0")
ci:    -> 0.0002s
ci: -- execute("        CREATE INDEX CONCURRENTLY IF NOT EXISTS index_issues_on_title_trigram ON issues\n          USING gin (title gin_trgm_ops) WITH (fastupdate='false')\n")
ci:    -> 0.0084s
ci: -- execute("RESET statement_timeout")
ci:    -> 0.0002s
ci: == 20221122063922 RemoveIssueTitleTrigramIndex: reverted (0.0102s) ============

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 #364556 (closed)