NFSD: Remove dead code in nfsd4_create_session()

Clean up. AFAICT, there is no way to reach the out_free_conn label
with @old set to a non-NULL value, so the expire_client(old) call
is never reached and can be removed.

Reviewed-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>