Remove redundant index_releases_on_author_id
In !71287 (merged) we introduced the new index index_releases_on_author_id_id_created_at
which covers the existing one.
So we can remove it.
The 17.0 major release is coming on May 16, 2024! This version brings many exciting improvements to GitLab, but also removes some deprecated features. We are introducing three breaking change windows during which we expect breaking changes to be deployed to GitLab.com. You can read more about it on our blogpost. The second breaking change window begins 2024-04-29 09:00 UTC and ends 2024-05-01 22:00 UTC.
In !71287 (merged) we introduced the new index index_releases_on_author_id_id_created_at
which covers the existing one.
So we can remove it.