platforms/drm: drop the double tap timer

This feature was implemented in commit a66eb1a5 earlier

Double tap wake up is not a feature to be implemented at compositor level but rather at the hardware/kernel level. Double tap timer here means when screen is turned off, libinput will continue to poll the touchscreen for new events. And that affects the power usage of the device.

double-tap-to-wakeup is generally interrupt at driver/hardware level which have ability to wake system up even from the sleep. We also eventually want to close the libinput fd (would need separate patch though), to allow for touchscreen device to go into power saving state using runtime_pm.