message: Log whenever a stream handler is removed
diff: @@ -650,6 +650,7 @@ bool scheduled_actor::finalize() {
  bool scheduled_actor::handle_stream_msg(mailbox_element& x,
  behavior* active_behavior) {
  + CAF_LOG_TRACE(CAF_ARG(x));
  CAF_ASSERT(x.content().match_elements<stream_msg>());
  auto& sm = x.content().get_mutable_as<stream_msg>(0);
  auto e = streams_.end();
  @@ -665,6 +666,9 @@ bool scheduled_actor::handle_stream_msg(mailbox_element& x,
  } else if (i != e) {
  if (i->second->done()) {
  streams_.erase(i);
  + CAF_LOG_DEBUG("Stream is done and could be safely erased"
  + << CAF_ARG(sm.sid) << ", remaining streams ="
  + << deep_to_string(streams_).c_str());
  if (streams_.empty() && !has_behavior())
  quit(exit_reason::normal);
  }
  