fix class references in vtkDataObject's documentation
fix class references in vtkDataObject's documentation

- vtkDataObjectToDataSet --> vtkDataObjectToDataSetFilter
- vtkDataObjectSource class was removed in bbe652a
- vtkDataObjectFilter class removed in 490657f
- vtkDataObjectMapper doesn't seem to ever have existed as a class (it was introduced to the documentation in d9f5c20)

keithroe/vtkoptix,SimVascular/VTK,SimVascular/VTK,keithroe/vtkoptix,keithroe/vtkoptix,keithroe/vtkoptix,keithroe/vtkoptix,SimVascular/VTK,SimVascular/VTK,SimVascular/VTK,SimVascular/VTK,keithroe/vtkoptix,SimVascular/VTK,SimVascular/VTK,keithroe/vtkoptix,keithroe/vtkoptix