Migration to remove disabled project mirrors
There is an open sec issue relating to project remote mirrors being disabled instead of destroyed. https://gitlab.com/gitlab-org/gitlab-ce/issues/54574
After the fix is merged (https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/10355) future mirrors are destroyed but there may be leftover mirrors in the DB that are disabled and not deleted.
The settings UI only shows enabled mirrors, so project owners will still not be able to see and delete their already disabled mirrors. There is no UI for toggling anymore so it should always show disabled mirrors.
Disabled push mirrors have to be manually deleted and disabled pull mirrors will only be reset after the project record updates. https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/10361
We should write a migration that removes disabled project mirrors, if possible, so we don't depend on project owners checking this setting themselves.
@DouweM
noted that we should probably clean up the repo remotes as well as remove the db rows.