Attempting to use a stable device path there does not actually work,
so we might as well remove it and hope that directfb can now automatically
detect the touchscreen for osk-sdl.
Most devices do not need to set any of these variables.
directfb can now automatically detect touchscreens, calibration is
only needed for resistive touchscreens and dev_keyboard is unused.
Automatically done using:
- sed -i '/deviceinfo_dev_keyboard=""/d' device-*/deviceinfo
- sed -i '/deviceinfo_dev_touchscreen=""/d' device-*/deviceinfo
- sed -i '/deviceinfo_dev_touchscreen_calibration=""/d' device-*/deviceinfo
