LU-1187 idl: remove obsolete directory split flags

The directory split functionality from the old CMD (pre-DNE)
feature was never usable in production, and was removed before
the DNE 2.4 release.  Remove old flags relating to this feature.

Test-Parameters: trivial
Signed-off-by: Andreas Dilger <andreas.dilger@intel.com>
Change-Id: I052ea57843ae67c18706a80221590924077bf46f
Reviewed-on: https://review.whamcloud.com/31700
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: James Simmons <uja.ornl@yahoo.com>
Reviewed-by: Lai Siyao <lai.siyao@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>