Restored hover states for notifications

Hover state colours were being interfered with by tintColor. They've now
being restored to work as originally intended without tintColor
ag/24745369. At the same time, pressed state stay suppressed - adding
tintColor to pressed state makes them indistinguishable from NO_STATE.
We're choosing to leave pressed state suppressed because of bugs
introduced by not suppressing it b/309221765.
A more permanent fix for this will be tracked in this issue b/313920497

Test: manual testing -> start swiping on notification -> ensure there is
no flicker. Hover over a notification with a mouse -> ensure hover
effect occurs as defined in uX Specs here go/notifications-hover-prototype

Fixes: 309221765
Flag: NA

Change-Id: Ibcfd9d243b2d3ba9816aff754331938d6b9c2390