Removes this object from a given category.

        :param Category category:
        :return:

def remove_from_category(self, category):
        """Removes this object from a given category.

        :param Category category:
        :return:
        """
        ctype = ContentType.objects.get_for_model(self)
        self.categories.model.objects.filter(category=category, content_type=ctype, object_id=self.id).delete()