Remove migration-related code in Container Repository
What does this MR do and why?
Issue: #409873
In this MR, we remove the backend code that is related to the migration of the container registry for Gitlab.com. The migration for Gitlab.com is now complete and now it is time for cleanup.
Several feature flags are also removed.
Database columns will be ignored and removed in succeeding MRs.
MR acceptance checklist
Related to #409873
Edited by Adie (she/her)