Remove all touch-screen-related code

It didn't work anymore, at all. Touchscreen polling occurred only
*after* waiting for a button had completed. So the touchscreen events,
if any, would be ignored until the user had pressed a button, possibly
firing off another action with that button press and forwarding the
touchscreen event to the next interface that got brought up as a
result.

Reusing this code and fixing it would require far more work than
rewriting everything anew with touchscreen devices in mind from the
beginning.