LU-12923 libcfs: Remove CLASSERT() for libcfs_private.h

LU-12923 libcfs: Remove CLASSERT() for libcfs_private.h

This patch removes final CLASSERT() define from file
libcfs/include/libcfs/libcfs_private.h. For compile
time assertion kernel defined BUILD_BUG_ON() is preferred

Test-Parameters: trivial
Signed-off-by: Arshad Hussain <arshad.super@gmail.com>
Change-Id: I6d7dd55489824631ae61393413598fe6dc4365a2
Reviewed-on: https://review.whamcloud.com/37188
Reviewed-by: James Simmons <jsimmons@infradead.org>
Reviewed-by: Petros Koutoupis <pkoutoupis@cray.com>
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Ben Evans <bevans@cray.com>
Reviewed-by: Shaun Tancheff <shaun.tancheff@hpe.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>