LU-1199 build: Remove obsolete check for 2.4 kernels

Remove check for 2.4 kernels, which are no longer supported.

Change-Id: I4ed5b7c2686fa9b0c104444853e45900f90e1eb8
Signed-off-by: Christopher J. Morrone <morrone2@llnl.gov>
Reviewed-on: http://review.whamcloud.com/4679


Tested-by: Hudson
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Brian J. Murrell <brian.murrell@intel.com>
Tested-by: Maloo <whamcloud.maloo@gmail.com>