message: Use more concise code to handle `BlockProposerAnnouncement`
diff: @@ -1122,16 +1122,16 @@ impl reactor::Reactor for Reactor {
  }
  ParticipatingEvent::BlockProposerAnnouncement(
  BlockProposerAnnouncement::DeploysExpired(hashes),
  - ) => {
  - let mut effects = Effects::new();
  - for hash in hashes {
  + ) => hashes
  + .into_iter()
  + .map(|hash| {
  let reactor_event = ParticipatingEvent::EventStreamServer(
  event_stream_server::Event::DeployExpired(hash),
  );
  - effects.extend(self.dispatch_event(effect_builder, rng, reactor_event));
  - }
  - effects
  - }
  + self.dispatch_event(effect_builder, rng, reactor_event)
  + })
  + .flatten()
  + .collect(),
  ParticipatingEvent::LinearChainAnnouncement(
  LinearChainAnnouncement::NewFinalitySignature(fs),
  ) => {
  