message: Unify `map` and `filter_map` calls.
diff: @@ -285,16 +285,14 @@ where
  let targeted_messages = messages
  .into_iter()
  - .map(|hwm| {
  + .filter_map(|hwm| {
  let delivery = self.delivery_time_strategy.gen_delay(
  rand,
  &hwm,
  &self.delivery_time_distribution,
  delivery_time,
  );
  - (hwm, delivery)
  - })
  - .filter_map(|(hwm, delivery)| match delivery {
  + match delivery {
  DeliverySchedule::Drop => {
  trace!("{:?} message is dropped.", hwm);
  None
  @@ -304,6 +302,7 @@ where
  let targeted = hwm.into_targeted(recipient);
  Some((targeted, timestamp))
  }
  + }
  })
  .collect();
  