COMP: Remove vtkMPIUtilities.h include

Removed include tro vtkMPIUtilities.h, which was only used for
debugging purposes. Further, vtkPVSessionCore should not include
anything MPI specific, b/c it would break non-mpi builds.

Change-Id: Ib6eccadaa317651d93db56571a3d49d5e1717c91
Merge topic 'use-gatherv-in-collect-information' into next

31bf38f4 COMP: Remove vtkMPIUtilities.h include