Enforce authentication_events retention policy by hard deleting rows and clean up archive workers

With the work in #545007 (closed) finished the 1 year retention policy for authentication_events is now being enforced.

The archiving infrastructure achieves a soft delete of records from authentication_events. This was only necessary during the initial phase of work as a rollout safety mechanism.

Now that the production authentication_events table has contained only rows within the retention policy for some time, we are confident that soft deletion is no longer necessary.

Proposal

• Delete Gitlab::BackgroundMigration::ArchiveAuthenticationEvents (!212674 (closed)) (!215101 (merged))
• Update Authn::DataRetention::AuthenticationEventArchiveWorker to stop inserting rows in authentication_event_archived_records, hard deleting rows from authentication_events instead. (!212677 (merged))
• Drop the authentication_event_archived_records table (!216011)