Remove TaskViewDrawable, scale RecentsView instead

Instead of faking recents scaling up when swiping down on a task,
actually scale it up. This is more consistent with what we do
for scaling to/from fullscreen elsewhere, and cleans up some code.

Bug: 130020567
Change-Id: I1a07813468d9a66f8f4e7b5d3d9a191b565f165c