Drop index `index_events_on_project_id_and_id_desc_on_merged_action` form events table
The events table has many indexes. We have found some, including index_events_on_project_id_and_id_desc_on_merged_action
, that are not used. This issue is to remove that index from the database.
By reducing the number of indexes on that table, it will help to mitigate another issue (gitlab-com/gl-infra/scalability#2301 (closed))
We just did this for a different table and wrote down the process we followed here: #402497 (closed)