Input: xpad - drop obsolete driver versioning

The driver version numbers and changelog have not been updated in a
long while to reflect actual changes. Remove the version number and
add a notice that later changes can be tracked in SCM.

Signed-off-by: Anssi Hannula <anssi.hannula@gmail.com>
Signed-off-by: Dmitry Torokhov <dtor@mail.ru>