LU-12477 libcfs: Remove obsolete config checks

LU-12477 libcfs: Remove obsolete config checks

Remove a few config checks for kernel versions we no longer
support. Only 3.10+ kernels are now supported.

Signed-off-by: Patrick Farrell <pfarrell@whamcloud.com>
Change-Id: I4f4177c512a37fb7a78bab69aa89aa7199ab30b4
Reviewed-on: https://review.whamcloud.com/35342
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: James Simmons <jsimmons@infradead.org>
Reviewed-by: Petros Koutoupis <pkoutoupis@cray.com>
Reviewed-by: Shaun Tancheff <stancheff@cray.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>