nfsd: nfs4_open_delegation needs to remove_stid rather than unhash_stid

In the out_free: path, the newly allocated stid must be removed rather
than unhashed so it can never be found.

Signed-off-by: Benny Halevy <bhalevy@primarydata.com>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>