Fix wrapping exclusion of enums in namespaces

The hierarchy files applied the WRAPEXCLUDE flag to all enums in namespaces, even though these enums are wrappable. In particular the vtkDICOM DC namespace enums were not properly wrapped for VTK 9.1, even though they had been wrapped for VTK 9.0 and earlier.

Reported in discourse: "vtk-9-1-python-overloaded-method-call-broken".