tablet: don't disable the proximity quirk on good sequences

There are tablets out there that *sometimes* send the right event sequence,
but are generally broken. So let's not disable that quirk even if we do get a
right sequence.

Affected devices: Lenovo Flex 5
Fixes #248
Fixes #290

Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>