[XFS] ktrace kt_lock is unused, remove it.

SGI-PV: 970382
SGI-Modid: xfs-linux-melb:xfs-kern:29747a

Signed-off-by: Eric Sandeen <sandeen@sandeen.net>
Signed-off-by: Donald Douwsma <donaldd@sgi.com>
Signed-off-by: Tim Shimmin <tes@sgi.com>