NFSv4: Remove nfs4_client->cl_sem from close() path

 We no longer need to worry about collisions between close() and the state
 recovery code, since the new close will automatically recheck the
 file state once it is done waiting on its sequence slot.

 Ditto for the nfs4_proc_locku() procedure.

Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>