def unregister_sizer(self, attr_name):
        if attr_name not in self._sizedimage_registry:
            raise NotRegistered(
                'No SizedImage subclass is registered to %s' % attr_name
            )
        else:
            del self._sizedimage_registry[attr_name]
Unregister the SizedImage subclass currently assigned to `attr_name`.
dataset/ETHPy150Open WGBH/django-versatileimagefield/versatileimagefield/registry.py/VersatileImageFieldRegistry.unregister_sizer