LU-2154 osp: osd-zfs: remove 2.3.x debugging code

LU-2154 osp: osd-zfs: remove 2.3.x debugging code

When LUSTRE_VERSION_CODE is increased beyond 2.3.90 the version
based debug code generates a compile warning and fails to build.
Originally added in commit 04e1d0cb95e1ad12 and 2acb75c36511aca9.

Since we have been running with these checks for months without
problem, and it will soon be inactivated anyway, we may as well
remove the code entirely instead of just fixing it.

Signed-off-by: Andreas Dilger <andreas.dilger@intel.com>
Change-Id: I1c104ef388f112c619d4ff4b7f00d17383500c1e
Reviewed-on: http://review.whamcloud.com/6219
Tested-by: Hudson
Reviewed-by: Nathaniel Clark <nathaniel.l.clark@intel.com>
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Alex Zhuravlev <alexey.zhuravlev@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>