collab: Drop `billing_events` table (#31131)

Marshall Bowers created

This PR drops the `billing_events` table, as we're no longer using it.

Release Notes:

- N/A

Change summary

crates/collab/migrations_llm/20250521222416_drop_billing_events_table.sql | 1 
1 file changed, 1 insertion(+)

Detailed changes