Removal of GetEstimatedMemorySize() method from vtkDataObject and vtkImageData

This method, which aimed to provide an estimate about memory use by a pipeline before execution, was partially and incorrectly implemented. Since it was not being used by VTK and since it was not fully implemented, it was removed in VTK 6. Those that relied on this functionality are advised to develop a more mature implementation by sub-classing one of the VTK executive classes.