Delete Git repository references on MR delete
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### Background
In https://gitlab.com/gitlab-org/gitlab/-/merge_requests/71493, it was explored that we can delete references created when a MR is created when that specific MR is deleted. This helps reduce the references in repository.
### Proposed Solution
Continue https://gitlab.com/gitlab-org/gitlab/-/merge_requests/71493 to apply suggestion made in https://gitlab.com/gitlab-org/gitlab/-/merge_requests/71493/diffs#note_1496380658 or create a new MR.
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