touchpad: rm dead tp_palm_tap_is_palm
This was added in 39f11253 (https://bugs.freedesktop.org/show_bug.cgi?id=89625)
Later, a more sophisticated palm detection was implemented in 46eab975 (https://bugs.freedesktop.org/show_bug.cgi?id=103210)
The only place where tp_palm_tap_is_palm()
is called is if the more
sophisticated palm detection has already decided that this is not a palm,
so it should never return true.
See also !878 (merged)