Removing custom dispatchDraw logic and letting the system handle

selecting appropriate children for drawing.

> System already skips children which are outside the bounds. Originally
this logic was added because workspace layout is larger than the screen, and
we need to selectivly skip more children. But over time we have added many
special conditions and at present workspace actually draws more children than
needed at any given time.
> Fixing bug, where onBeginPageMoving was getting called during folder open

Bug: 12116740
Change-Id: Idee18ee9cd9d348ebc4dfd82f4ff6df14e0d22d2