Removed round rect clipping and hardware layers from recents

This saves us a lot of memory and we avoid the clipToOutline.
The view still looks the same, as we now draw the thumbnail
in a rounded rect.
We now only use a hardware layer on the header, which is much
smaller.

Bug: 17522143
Change-Id: I197a1172efe8450ffb0b537c780a240d38f84275