Remove usage of the nlohmannjson library from public facing API

The nlohmann::json vtkAbstractArray::SerializeValues() method is now removed as the public exposure of VTK’s vendored nlohmannjson library caused difficulty for downstream projects that link to a different nlohmannjson.

These methods were added in vtk/vtk!11163 which was released in 9.4. That merge request has now been reverted. These methods are removed (instead of deprecation) because deprecation would prevent fixing the problem.