Drop non-partitioned `audit_events_archived` table [RUN ALL RSPEC] [RUN AS-IF-FOSS]

What does this MR do?

This is the last step of partitioning audit_events. We're now removing the non-partitioned archive table.

We have swapped tables and introduced the AuditEventsArchived model with 0dd449a8.

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Availability and Testing

We should be extra careful about this table not being used anymore from the application.