vtkStructuredGridVolumeRepresentation no longer users the vtkExtentTranslator
provided by the pipeline to determine the piece-extent mapping. Instead it
explicitly determines that using parallel communication. Although this is not
essential currently, with forthcoming VTK changes, this will become essential
i.e. not relying on the extent translator from the pipeline.

Change-Id: I61ec582b7d7dc291f0da779489153b62411c4c26