message: Remove false check on stream handshake results
diff: @@ -61,11 +61,7 @@ auto stream_msg_visitor::operator()(stream_msg::open& x) -> result_type {
  return fail(sec::stream_init_failed);
  }
  // Invoke behavior of parent to perform handshake.
  - auto res = (*bhvr_)(x.msg);
  - if (!res) {
  - CAF_LOG_WARNING("actor did not respond to handshake:" << CAF_ARG(x.msg));
  - return fail(sec::stream_init_failed);
  - }
  + (*bhvr_)(x.msg);
  if (self_->streams().count(sid_) == 0) {
  CAF_LOG_WARNING("actor did not provide a stream "
  "handler after receiving handshake:"
  