Remove the vtkSetNGetMacro from vtkSetGet.h

The original purpose of vtkSetNGetMacro was to make a "set/get" macro
that could be used with classes that were not derived from vtkObjectBase
(and that therefore could use vtkSetMacro and vtkGetMacro).  However,
some developers were assuming that it was simply a shorthand that
combined the vtkSetMacro and vtkGetMacro, but it does not call Modified
as is required when setting properties of a vtkObjectBase-derived object.

This macro was added after VTK 5.10 was released, so there should be no
backward compatility problems with its removal.

Change-Id: I5fe74fc52814ac6b7f6bc67f79d2880e2fd1d16a
Merge topic 'remove-vtksetnget' into master

f2d1b35b Remove the vtkSetNGetMacro from vtkSetGet.h