Why CUDS._is_dataset is defined as a staticmethod?

[dpinte]

What is the purpose of having a static private method on the CUDS class?

https://github.com/simphony/simphony-common/blob/master/simphony/cuds/cuds.py#L41

    @staticmethod
    def _is_dataset(obj):
        """Check if the object is a dataset."""
        return isinstance(obj, (ABCDataset,
                                api.DataSet))

This should be removed and replaced by the appropriate function.