Drop hack for drivers that emit zero ABS_MT_TOUCH_MAJOR.

Bug: 5064702

When using Linux MT Protocol A, drivers are supposed to omit
fingers that go up and to send an empty sync with no fingers
(can be just an SYN_MT_REPORT / SYN_REPORT) when no fingers
remain.

This makes Android more compliant with the protocol standard.

Change-Id: I5775feb14ab7db015824a32b1e2c015da239385d