quirks: fix Apple external trackpad v2 thresholds
The external Apple "Magic" trackpads, both the first and the second
generations, have pretty good built-in spurious touch filtering. For
these device models libinput's own filtering is not required. Using low
enough values such as 20:10 for AttrTouchSizeRange
effectively disables libinput's filtering.
Fixes #280 (closed)