staging/lustre: Get rid of LIBLUSTRE_CLIENT and its users

This define only made sense in a userspace library client, not in the kernel.

Signed-off-by: Oleg Drokin <green@linuxhacker.ru>
Reviewed-by: James Simmons <jsimmons@infradead.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>