remove gitlab-pre-container-registry bucket in pre

In https://gitlab.com/gitlab-com/gl-infra/infrastructure/-/issues/12763 we created a new storage bucket gitlab-pre-container-registry for pre and migrated over to it. But then we changed the migration approach to do the migration within the old bucket instead of to a new one, so we never did the same for gstg and gprd.

We should migrate back to the old bucket in pre and remove the new bucket, to have pre, gstg and gprd use the same setup.