touchpad: drop distance threshold to detect pinches

touchpad: drop distance threshold to detect pinches

This gives us too many false positives of 2fg scroll being detected as pinch
gesture. Reporter in [1] uses index+ring finger and thus exceeds the distance
easily (that's admittedly a special case).

This is worsed by the lack of a client stack that handles the gestures. User's
don't see that they're inadvertently performing a gesture, they just see 2fg
scroll not working.

Drop the distance for now, once we have a ubiquitous client stack we can
revisit and bring it back.

[1] https://bugzilla.redhat.com/show_bug.cgi?id=1246868

Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>
Reviewed-by: Hans de Goede <hdegoede@redhat.com>