evdev: Discard events from a touchscreen paired with an unplugged output

evdev: Discard events from a touchscreen paired with an unplugged output

Commit 17bccaed intended to make the events coming from a touchscreen
paired with an unplugged output to be discarded, while an unpaired one
would just choose a different output. However, the logic was inverted
causing the opposite to happen.

Later in commit 161c6c56, the default behavior was changed to map an
output to a default output if the one specified via udev is not
present. This change is reverted by this patch.

v2: undo the change from commit 161c6c56.

v3: deal with libinput too.