General cleanup in vtkOrderedCompositeDistributor.

vtkOrderedCompositeDistributor no longer needs the caching logic. Cleaning it up
to make the code easier.

Change-Id: Ibad7e18ee5f098bd493ccc71f15ef57da6fddfce
Merge topic 'cleanup_vtkOrderedCompositeDistributor' into next

8c35f37 General cleanup in vtkOrderedCompositeDistributor.