DROP temp_notes_backup table

What does this MR do and why?

The table was introduced as a safety measure to prevent data loss in !146023 (merged) release 16.10. Safe to remove after several releases with no reports of data loss. As described in !146023 (merged) there were only 1.6K backed up records which is a very small amount considering the size of the notes table

MR acceptance checklist

Please evaluate this MR against the MR acceptance checklist. It helps you analyze changes to reduce risks in quality, performance, reliability, security, and maintainability.

Migration output

UP

bin/rails db:migrate
main: == [advisory_lock_connection] object_id: 125740, pg_backend_pid: 14924
main: == 20240527213416 DropTempNotesBackupTable: migrating =========================
main: -- drop_table(:temp_notes_backup)
main:    -> 0.0008s
main: == 20240527213416 DropTempNotesBackupTable: migrated (0.0035s) ================

main: == [advisory_lock_connection] object_id: 125740, pg_backend_pid: 14924
ci: == [advisory_lock_connection] object_id: 125980, pg_backend_pid: 14926
ci: == 20240527213416 DropTempNotesBackupTable: migrating =========================
ci: -- drop_table(:temp_notes_backup)
ci:    -> 0.0008s
ci: == 20240527213416 DropTempNotesBackupTable: migrated (0.0066s) ================

ci: == [advisory_lock_connection] object_id: 125980, pg_backend_pid: 14926

DOWN

bin/rails db:rollback:main db:rollback:ci
main: == [advisory_lock_connection] object_id: 125340, pg_backend_pid: 13559
main: == 20240527213416 DropTempNotesBackupTable: reverting =========================
main: -- execute("CREATE TABLE IF NOT EXISTS temp_notes_backup (LIKE notes);")
main:    -> 0.0075s
main: -- execute("ALTER TABLE temp_notes_backup ADD PRIMARY KEY (id);")
main:    -> 0.0024s
main: == 20240527213416 DropTempNotesBackupTable: reverted (0.0295s) ================

main: == [advisory_lock_connection] object_id: 125340, pg_backend_pid: 13559
ci: == [advisory_lock_connection] object_id: 126300, pg_backend_pid: 13808
ci: == 20240527213416 DropTempNotesBackupTable: reverting =========================
ci: -- execute("CREATE TABLE IF NOT EXISTS temp_notes_backup (LIKE notes);")
ci:    -> 0.0066s
ci: -- execute("ALTER TABLE temp_notes_backup ADD PRIMARY KEY (id);")
ci:    -> 0.0017s
ci: == 20240527213416 DropTempNotesBackupTable: reverted (0.0156s) ================

ci: == [advisory_lock_connection] object_id: 126300, pg_backend_pid: 13808

Related to #443667 (closed)