Investigate dropping idx_projects_on_repository_storage_last_repository_update_ccnew

As part of reducing lightweight lock contention, investigate if it's possible to drop the index idx_projects_on_repository_storage_last_repository_update_ccnew from the projects table

• Find out when and why the index was added
• Decide if the index can be dropped
• Drop the index if possible
• If the index cannot be dropped, document the reason in a comment on this issue and close.