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: