Address drag unreliability during touch exploration

The code was trying to set the location of the drag, but MotionEvent doesn't behave consistently when setting a single location to a multi-touch event.

All that's needed is to select the correct pointer, so removing messing with the location gives more consistent behavior.

Bug: 163105030
Change-Id: I6c315cf0a1e48847cc778ec8c34b382d13ce3555
Test: Manually testing at this point of the passthrough, and relying on treehugger.