Clean up duplicate indexes
## Description
After https://gitlab.com/gitlab-org/gitlab/-/issues/385701, we can identify duplicated indexes. At the moment, there are many duplicate btree indexes that can be removed from our database, as they are not needed anymore.
The list of duplicated indexes can be found in the [`duplicate_indexes.yml`](https://gitlab.com/gitlab-org/gitlab/-/blob/master/spec/support/helpers/database/duplicate_indexes.yml) file.
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