Input: elantech - remove support for proprietary X driver

Apparently somewhere someone had a proprietary X driver. To get the
multitouch info, it uses some hack on the normal API instead of using
the multitouch protocol. Now that the multitouch info is transmitted
correctly it makes not much sense to keep it. Especially because it's
impossible to find this proprietary X driver anywhere, so the number of
users must be very low.

Signed-off-by: Éric Piel <eric.piel@tremplin-utc.net>
Reviewed-by: Henrik Rydberg <rydberg@euromail.se>
Signed-off-by: Dmitry Torokhov <dtor@mail.ru>