message: Remove unnecessary event loop proxy `Mutex`
  I am not sure why I had to use it in the first place...
diff: @@ -469,17 +469,12 @@ impl Subscriptions {
  futures::channel::mpsc::channel(100);
  let stream = recipe.stream(event_receiver);
  -
  - // TODO: Find out how to avoid using a mutex here
  - let proxy =
  - std::sync::Arc::new(std::sync::Mutex::new(proxy.clone()));
  + let proxy = proxy.clone();
  let future = futures::future::select(
  cancelled,
  stream.for_each(move |message| {
  proxy
  - .lock()
  - .expect("Acquire event loop proxy lock")
  .send_event(message)
  .expect("Send subscription result to event loop");
  