ENH: Remove VTK 4 backwards compatibility

Removed vtkSource, vtkProcessObject and subclasses.
http://www.vtk.org/Wiki/VTK/VTK_6_Migration/Overview#Removal_of_VTK_4_Backwards_Compatibility_Superclasses
http://www.vtk.org/Wiki/VTK/Tutorials/New_Pipeline#Converting_an_Existing_Filter_to_the_New_Pipeline

Closes #3485
From Yuzheng Zhou <yuzheng.zhou@kitware.com>

git-svn-id: http://svn.slicer.org/Slicer4/trunk@23119 3bd1e089-480b-0410-8dfb-8563597acbee