Removed hashed storage migration workers [Second minor release]
Context
GitLab's early versions organized the Git storage by replicating the same mapping structure from the projects URLs. After GitLab v10, we made an initiative to migrate the legacy git storage to new Hashed Storage structure. We added a bunch of rake tasks, and workers to support this migration. In Gitlab 13.4.0, we introduced a background migration to migrate legacy storage to object storage. After this version, newly created projects also use new hashed storage. It means since GitLab 14.0, there won't be any projects with legacy storage and it's sure that there won't be any jobs of those workers in the backlog. As soon as the self-managed instances follow upgrade path or major version release, the migration utilities are no longer meaningful to them. It's time to remove those scripts to clean up the code base.
Now that !133394 (merged) is merged, we should remove the workers following the steps in Sidekiq compatibility across updates.