Input: elantech - remove module parameter force_elantech

This essentially reverts commit f81bc788.

With recent work on elantech driver, I believe we now have complete support
for all elantech touchpads. So remove this hack.

Signed-off-by: JJ Ding <jj_ding@emc.com.tw>
Reviewed-by: Éric Piel <eric.piel@tremplin-utc.net>
Signed-off-by: Dmitry Torokhov <dtor@mail.ru>