NFS: Fix old dentry rehash after move

Now that nfs_rename()'s d_move has moved within the RPC task's rpc_call_done
callback, rehashing new_dentry will actually rehash the old dentry's name
in nfs_rename().  d_move() is going to rehash the new dentry for us anyway,
so doing it again here is unnecessary.

Reported-by: Chuck Lever <chuck.lever@oracle.com>
Fixes: 920b4530

 ("NFS: nfs_rename() handle -ERESTARTSYS dentry left behind")
Signed-off-by: Benjamin Coddington <bcodding@redhat.com>
Tested-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>