vtkCompositePolyDataMapper2: Fix infinitely growing 'RenderedList'

vtkCompositePolyDataMapper2Helper maintained a secondary data structure called "RendereredList" which was populate with same values available in another ivar called "Data". However, when items from "Data" were removed, the code didn't update "RendereredList" similary causing "RendereredList" to grow infinitely.

To reproduce, one could simply monitor the size of "Renderered" and end of vtkCompositePolyDataMapper2::Render for a time-varying dataset and you'd notice it kept growing.

Fixed by not keeping this duplicate datastricture in vtkCompositePolyDataMapper2Helper. When needed, the rendered list is now simply generated using the values in "Data".

(cherry picked from commit 18d10d0e)