LU-4278 libcfs: remove LWT

LU-4278 libcfs: remove LWT

The LWT code has been disabled on all platforms since being merged.
Now that its functionality can be replaces by Systemtap etc, it is
on longer needed.

Signed-off-by: Peng Tao <bergwolf@gmail.com>
Change-Id: I21dc913bfdbbf1bfba5e0d7de3d43b183f0e5b23
Reviewed-on: http://review.whamcloud.com/8340
Reviewed-by: Dmitry Eremin <dmitry.eremin@intel.com>
Reviewed-by: James Simmons <uja.ornl@gmail.com>
Reviewed-by: John L. Hammond <john.hammond@intel.com>
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>