message: thread synchronizer: fix assertion
  The other thread can already have entered the wait.
diff: @@ -63,7 +63,6 @@ void ThreadSynchronizer::syncPointWorker(absl::string_view event_name) {
  void ThreadSynchronizer::barrierOnWorker(absl::string_view event_name) {
  SynchronizerEntry& entry = getOrCreateEntry(event_name);
  absl::MutexLock lock(&entry.mutex_);
  - ASSERT(!entry.at_barrier_ && entry.wait_on_);
  ENVOY_LOG(debug, "thread synchronizer: barrier on {}", event_name);
  entry.mutex_.Await(absl::Condition(&entry.at_barrier_));
  ENVOY_LOG(debug, "thread synchronizer: barrier complete {}", event_name);
  