LU-936 Remove LUSTRE_KERNEL_VERSION

LU-936 Remove LUSTRE_KERNEL_VERSION

Patched kernels are no longer an absolute requirement for
Lustre servers.  Remove the LC_LUSTRE_VERSION_H autoconf
check and all usage of the LUSTRE_KERNEL_VERSION #define.
Going forward any specific kernel dependency should be
expressed with an explicit, clearly documented, autoconf
test.

As part of this change the check for automatically disabling
lustre server support has been moved to the ldiskfs autoconf
checks.  Previously this was done by checking for the
existance of a patched kernel.

Change-Id: Ifb5dcaf62638146a190f5d7417b9462177c5730d
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-on: http://review.whamcloud.com/1873
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Tested-by: Hudson
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>