Remove a previously registered callback

        :param str name: Hook name
        :param callable func: A function reference\
        that was registered previously

def unregister(self, name, func):
        """
        Remove a previously registered callback

        :param str name: Hook name
        :param callable func: A function reference\
        that was registered previously
        """
        try:
            templatehook = self._registry[name]
        except KeyError:
            return

        templatehook.unregister(func)