Revert "keyboard: Handle touch events"

This reverts commit a84fb99c0aca9fd6eeb83a270c48113133e89de2.

This commit didn't make the OSK fully operational yet on Wayland, and
caused the double emission of key events on X11 due to the OSK keys
receiving first touch events from the passive touch grab, and then
emulated pointer events from event selection after the touch sequence
was rejected in the grab.

When we make a better effort at handling touch events just once on X11,
this commit can be reapplied and remaining wayland OSK support resumed
from there. In the mean time, this patch is better reverted.

https://bugzilla.gnome.org/show_bug.cgi?id=735681
Makefile: Use $(NULL) in one more place
wobbly