Draft: Drop authentication_event_archived_records table

What does this MR do and why?

Drop the authentication_event_archived_records table. Last step in #562154.

• Table was added in 18.5: !202447 (merged)
• All references to this table were removed in 18.7
  • ArchiveAuthenticationEvents BBM: !215101 (merged)
  • AuthenticationEventArchiveWorker worker: !212677 (merged)
• Since there are no remaining references, and we've waited 1 milestone since removing table references, this should be safe to drop.

References

• Issue: #562154
• Table added: #562154
• Referencing BBM removed: !215101 (merged)
• References removed from recurring worker updated: !212677 (merged)

Screenshots or screen recordings

How to set up and validate locally

Migration output

`bin/rails db:migrate:up`

% bin/rails db:migrate:up:main VERSION=20251210170044

main: == [advisory_lock_connection] object_id: 131020, pg_backend_pid: 39248
main: == 20251210170044 DropAuthenticationEventArchivedRecords: migrating ===========
main: -- drop_table(:authentication_event_archived_records, {:if_exists=>true})
main:    -> 0.0732s
main: == 20251210170044 DropAuthenticationEventArchivedRecords: migrated (0.0914s) ==

main: == [advisory_lock_connection] object_id: 131020, pg_backend_pid: 39248

`bin/rails db:migrate:down`

% bin/rails db:migrate:down:main VERSION=20251210170044

main: == [advisory_lock_connection] object_id: 131000, pg_backend_pid: 42200
main: == 20251210170044 DropAuthenticationEventArchivedRecords: reverting ===========
main: -- create_table(:authentication_event_archived_records, {:id=>false})
main:    -> 0.0037s
main: -- execute("ALTER TABLE authentication_event_archived_records ADD PRIMARY KEY (id)")
main:    -> 0.0011s
main: -- transaction_open?(nil)
main:    -> 0.0000s
main: -- transaction_open?(nil)
main:    -> 0.0000s
main: -- execute("ALTER TABLE authentication_event_archived_records\nADD CONSTRAINT check_3b5f782c5d\nCHECK ( char_length(user_name) <= 255 )\nNOT VALID;\n")
main:    -> 0.0004s
main: -- execute("SET statement_timeout TO 0")
main:    -> 0.0002s
main: -- execute("ALTER TABLE authentication_event_archived_records VALIDATE CONSTRAINT check_3b5f782c5d;")
main:    -> 0.0004s
main: -- execute("RESET statement_timeout")
main:    -> 0.0003s
main: -- transaction_open?(nil)
main:    -> 0.0000s
main: -- transaction_open?(nil)
main:    -> 0.0000s
main: -- execute("ALTER TABLE authentication_event_archived_records\nADD CONSTRAINT check_0a55f02112\nCHECK ( char_length(provider) <= 64 )\nNOT VALID;\n")
main:    -> 0.0003s
main: -- execute("ALTER TABLE authentication_event_archived_records VALIDATE CONSTRAINT check_0a55f02112;")
main:    -> 0.0005s
main: == 20251210170044 DropAuthenticationEventArchivedRecords: reverted (0.0866s) ==

main: == [advisory_lock_connection] object_id: 131000, pg_backend_pid: 42200

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Related to #562154