LU-5596 lnet: Remove obsolete LNET variable

LU-5596 lnet: Remove obsolete LNET variable

For Lustre version 2.6.50 and later, the variable
session_features is defined as "LST_FEATS_MASK". For
earlier versions of Lustre, the same variable is defined
as "LST_FEATS_EMPTY.

Since Lustre master is at 2.6.52 or later, the second
definition of "session_features" can be removed.

Signed-off-by: James Nunez <james.a.nunez@intel.com>
Change-Id: I52e7a914880509cfcd4961032ab7775bbaf626a8
Reviewed-on: http://review.whamcloud.com/11825
Tested-by: Jenkins
Reviewed-by: Isaac Huang <he.huang@intel.com>
Reviewed-by: Doug Oucharek <doug.s.oucharek@intel.com>
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>