Combine vtk_wrap_python and vtk_wrap_python3.
The vtk_wrap_python macro was a copy-paste of vtk_wrap_python3. It makes more sense for vtk_wrap_python to call vtk_wrap_python3.
The vtk_wrap_python macro was a copy-paste of vtk_wrap_python3. It makes more sense for vtk_wrap_python to call vtk_wrap_python3.