LU-12477 kernel: eliminate lustre_patchless_compat.h

LU-12477 kernel: eliminate lustre_patchless_compat.h

Now that kernels earlier than RHEL7 3.11 series are no longer
support we can remove the wrapper related to the header
lustre_patchless_compat.h. With that gone the header can also
be removed.

Change-Id: I496983d3065fdd0718871548aeed6bf50fd0747b
Signed-off-by: James Simmons <uja.ornl@yahoo.com>
Reviewed-on: https://review.whamcloud.com/35539
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Shaun Tancheff <stancheff@cray.com>
Reviewed-by: Yang Sheng <ys@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>