LU-8823 ptlrpc: remove obsolete OST/MDT thread parameters

LU-8823 ptlrpc: remove obsolete OST/MDT thread parameters

The mdt_num_threads parameter was only briefly available from 2.0-2.2,
while mds_num_threads has been available since 1.x to control the
number of service threads on the MDS respectively.  A warning message
is printed on startup since 2.3 if mdt_num_threads parameters were in
use, so there shouldn't be any users anymore.

The ost_num_threads parameter has been deprecated since 1.6 or so.

Signed-off-by: Andreas Dilger <andreas.dilger@intel.com>
Change-Id: I587a1f3e4629d304412006a0f0e9fc1daeacab07
Reviewed-on: https://review.whamcloud.com/23705
Reviewed-by: Patrick Farrell <paf@cray.com>
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Bob Glossman <bob.glossman@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>