Remove event handler `handler` from registered handlers of the engine

        Args:
            handler (callable): the callable event handler that should be removed
            event_name: The event the handler attached to.

def remove_event_handler(self, handler, event_name):
        """Remove event handler `handler` from registered handlers of the engine

        Args:
            handler (callable): the callable event handler that should be removed
            event_name: The event the handler attached to.

        """
        if event_name not in self._event_handlers:
            raise ValueError("Input event name '{}' does not exist".format(event_name))

        new_event_handlers = [(h, args, kwargs) for h, args, kwargs in self._event_handlers[event_name]
                              if h != handler]
        if len(new_event_handlers) == len(self._event_handlers[event_name]):
            raise ValueError("Input handler '{}' is not found among registered event handlers".format(handler))
        self._event_handlers[event_name] = new_event_handlers