Don't garbage collect commits that have related DB records like comments
Closes #13524 (closed)
Also needed for https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/4101.
Do not update/delete: Banner broadcast message test data
Do not update/delete: Notification broadcast message test data
Closes #13524 (closed)
Also needed for https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/4101.