Drop index index_projects_aimed_for_deletion

See the description of !134438 (merged) for details.

We added a new index index_projects_id_for_aimed_for_deletion in !134438 (merged), that could help us replace an existing index index_projects_aimed_for_deletion.

Steps:

• Make sure all queries where the index index_projects_id_for_aimed_for_deletion is currently used can be covered by the new index index_projects_id_for_aimed_for_deletion.
• If so, delete the index index_projects_id_for_aimed_for_deletion