nfsd4: release openowners on free in >=4.1 case

We don't need to keep openowners around in the >=4.1 case, because they
aren't needed to handle CLOSE replays any more (that's a problem for
sessions).  And doing so causes unexpected failures on a subsequent
destroy_clientid to fail.

We probably also need something comparable for lock owners on last
unlock.

Signed-off-by: J. Bruce Fields <bfields@redhat.com>