NFS: remove l_pid field from nfs_lockowner

this field is not used in any important way and probably should
have been removed by

Commit: 8003d3c4aa ("nfs4: treat lock owners as opaque values")

which removed the pid argument from nfs4_get_lock_state.

Except in unusual and uninteresting cases, two threads with the same
->tgid will have the same ->files pointer, so keeping them both
for comparison brings no benefit.

Acked-by: Jeff Layton <jlayton@redhat.com>
Signed-off-by: NeilBrown <neilb@suse.com>
Reviewed-by: Jeff Layton <jlayton@redhat.com>
Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com>

fs/nfs/nfs4proc.c

@@ -2947,7 +2947,6 @@ static int _nfs4_do_setattr(struct inode *inode,
 	} else if (truncate && state != NULL) {
 		struct nfs_lockowner lockowner = {
 			.l_owner = current->files,
-			.l_pid = current->tgid,
 		};
 		if (!nfs4_valid_open_stateid(state))
 			return -EBADF;