Remove unnecessary onCancel

When dragging up to bouncer, then canceling by letting your finger
go, the onCancel was setting the alpha to 0, to be immediately
followed by 1, causing a flicker.

Fixes: 406997667
Test: manual - drag and let go, observe
Flag: EXEMPT bugfix
Change-Id: Iae50d78ffeee9d9ba9d325682744f368a04c708e