LU-12477 lustre: remove obsolete config checks

LU-12477 lustre: remove obsolete config checks

Remove from the lustre kernel code all the support for kernels
earlier than the RHEL7 3.10+. This greatly simplifies the code
and makes build times much better.

Change-Id: If52091ac5249b2719b992032040ccf30cc5bf0e4
Signed-off-by: James Simmons <jsimmons@infradead.org>
Reviewed-on: https://review.whamcloud.com/37085
Reviewed-by: Shaun Tancheff <shaun.tancheff@hpe.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Petros Koutoupis <petros.koutoupis@hpe.com>
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Yang Sheng <ys@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>