Remove viewport display ID assignment in pointer mode

TouchInputMapper#dispatchPointerSimple() is only called when DeviceMode
is POINTER, which by definition is to dispatch events to cursor
position. Therefore it should always use the display from
PointerController. It's already doing that in the line 3446 so remove
this no-op line of code.

Test: Mouse click still works.
Change-Id: Id72bc37e75f42c52e121bfb50bfbf59b3717c66b