input: do not forward unmatched touch-ups

Commit a30e29af introduced the code to
deal with a touchscreen with touches already down when Weston starts
using it. It fixed the touchpoint counting problem.

However, Weston still should not forward or process the unmatched
touch-ups either. Code inspection says it would confuse the
idle-inhibit counting, and it could probably confuse clients as well.
Hence, just drop unmatched touch-ups.

Enhance the warning message to allow identifying where the event came
from.

v2:
- use syspath instead of devpath

Signed-off-by: Pekka Paalanen <pekka.paalanen@collabora.co.uk>
v1 Reviewed-by: Peter Hutterer <peter.hutterer@who-t.net>
v1 Tested-by: Matt Hoosier <matt.hoosier@gmail.com>
Reviewed-by: Peter Hutterer <peter.hutterer@who-t.net>