LU-2470 procfs: Remove unused lu_time code.

LU-2470 procfs: Remove unused lu_time code.

Remove lu_time.{c,h}, the unused wrappers for the functions defined
therein, and the stats file /proc/fs/lustre/mdt/*/site_time.

Signed-off-by: John L. Hammond <jhammond@tacc.utexas.edu>
Change-Id: Id45b12efd06134048a96f4b0ba92eaa4fce0b55d
Reviewed-on: http://review.whamcloud.com/4802
Tested-by: Hudson
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Reviewed-by: Keith Mannthey <keith.mannthey@intel.com>
Tested-by: Maloo <whamcloud.maloo@gmail.com>