message: Fix drop behavior of stream_distribution_tree
diff: @@ -114,9 +114,7 @@ public:
  void handle(stream_slots slots, upstream_msg::drop& x) override {
  CAF_LOG_TRACE(CAF_ARG(slots) << CAF_ARG(x));
  CAF_IGNORE_UNUSED(x);
  - auto slot = slots.receiver;
  - if (out().remove_path(slots.receiver, none, true))
  - policy_.path_dropped(slot);
  + super::handle(slots, x);
  }
  void handle(stream_slots slots, upstream_msg::forced_drop& x) override {
  