Fix redundant listen

Author: njxue

backend/user-service/index.js

@@ -105,9 +105,5 @@ app.use((req, res, next) => {
 
 app.use(errorHandler);
 
-app.listen(port, async () => {
-  console.log(`Server is running at http://localhost:${port}`);
-});
-
 export default app;
 export { port };