Making code more readable by removing global variable used for optimizations

Using the stack was more efficient because it prevented the creation
of new rectangles but it makes the code harder to read and prone to
bugs if the global state of the stack of rectangles gets corrupted
in any way.

When this optimization was written in 2008 it was necessary but now I
don't think it would have a big impact. The stack size is on average
of 30 and the rectangles are only created when doing the reorder which
runs about once per second if the user moves the finger too quickly.

Bug: 188081026
Test: atest ReorderWidgets
Change-Id: I35d8ee8d92f01035e72fe5763a7de47f4b6a73de