staging/lustre: Remove unused LUSTRE_VERSION_ALLOWED_OFFSET define

LUSTRE_VERSION_ALLOWED_OFFSET is only used on the server to disallow
connection of old userspace clients.

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