xfs: remove a stale comment from xfs_file_aio_write_checks()

The comment in xfs_file_aio_write_checks() about calling file_modified()
after dropping the ilock doesn't make sense, because the code that
unconditionally acquires and drops the ilock was removed by
commit 467f78992a ("xfs: reduce ilock hold times in
xfs_file_aio_write_checks").

Remove this outdated comment.

Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Eric Biggers <ebiggers@google.com>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>

fs/xfs/xfs_file.c

@@ -389,12 +389,6 @@ restart:
 	} else
 		spin_unlock(&ip->i_flags_lock);
 
-	/*
-	 * Updating the timestamps will grab the ilock again from
-	 * xfs_fs_dirty_inode, so we have to call it after dropping the
-	 * lock above.  Eventually we should look into a way to avoid
-	 * the pointless lock roundtrip.
-	 */
 	return file_modified(file);
 }