Delete the stored mapping of a reference.

        :param opaque_ref:       Reference which should be removed.
        :param bool global_ref:  Whether opaque_ref is a local or global
                                 reference.

def delete_reference(self, opaque_ref, global_ref=False):
        """
        Delete the stored mapping of a reference.

        :param opaque_ref:       Reference which should be removed.
        :param bool global_ref:  Whether opaque_ref is a local or global
                                 reference.
        """
        opaque_ref_value = self._get_reference_value(opaque_ref)
        if global_ref:
            del self.global_refs[opaque_ref_value]
        else:
            del self.local_refs[opaque_ref_value]