xfs: remove iolock lock classes

Content-Disposition: inline; filename=xfs-remove-iolock-classes

Now that we never take the iolock during inode reclaim we don't need
to play games with lock classes.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Rich Johnston <rjohnston@sgi.com>
Signed-off-by: Ben Myers <bpm@sgi.com>