rabbitmq: Cut redundant `stop_ioloop_on_close` parameter.

The default value of this parameter is already False upstream.
(It was already False in pika version 0.9.6, which we were
supposedly using when we introduced this in 4baeaaa52; not sure
what the story was there.)

zerver/lib/queue.py

@@ -187,7 +187,7 @@ class TornadoQueueClient(SimpleQueueClient):
         self.connection = ExceptionFreeTornadoConnection(
             self._get_parameters(),
             on_open_callback = self._on_open,
-            stop_ioloop_on_close = False)
+        )
         self.connection.add_on_close_callback(self._on_connection_closed)
 
     def _reconnect(self) -> None: