Revert "LU-6206 ptlrpc: start minimum service threads"

Revert "LU-6206 ptlrpc: start minimum service threads"

This is causing test failures in conf-sanity test_53b,
as seen in LU-6563.

This reverts commit cafa669a43062c5097d40803b9ba14e66edbae25.

Change-Id: I9935bb4d84fda7a9219818c20daa683954dcd0d7
Reviewed-on: http://review.whamcloud.com/14682
Reviewed-by: Jian Yu <jian.yu@intel.com>
Reviewed-by: John L. Hammond <john.hammond@intel.com>
Tested-by: Jenkins
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Tested-by: Andreas Dilger <andreas.dilger@intel.com>