Fix group destroy not working with Gitaly Cluster

Previously when a namespace was deleted, it would always attempt to remove the legacy storage path. For example, for namespace test-group, Rails would issue a removal for /path/to/test-group just in case there is data there.

If the path does not exist, Gitaly raises an Invalid Argument GRPC (3) exception, but Gitaly Cluster raises an Internal error (13).

Since hashed storage is now the default and the legacy path shouldn't be used at all, we can avoid this error entirely by not attempting to delete the legacy path.

Closes #276501 (closed)