docs(server-api): remove misleading note

Broadcasting with acknowledgements are supported since version 4.5.0.

Reference: https://socket.io/docs/v4/changelog/4.5.0#broadcast-and-expect-multiple-acknowledgements

Related: socketio/socket.io#5333

Author: darrachequesne

docs/server-api.md

@@ -2280,8 +2280,6 @@ io.on("connection", (socket) => {
 });
 ```
 
-**Note:** acknowledgements are not supported when broadcasting.
-
 #### socket.use(fn)
 
 <details className="changelog">