Related issue: https://gitlab.com/gitlab-org/gitlab/issues/195881

This removes indexes that we don't need anymore after changing the "tie
breaker" sorting direction. The indexes have been introduced with
https://gitlab.com/gitlab-org/gitlab/merge_requests/22623 to optimally
support the requests. This is not needed anymore since the tie breaker
now also changes its sorting direction.

For more details please refer to
https://gitlab.com/gitlab-org/gitlab/-/merge_requests/22623.

I've validated that these indexes are not being used on GitLab.com
anymore:
https://gitlab.com/gitlab-org/gitlab/issues/195881#note_278816057