message: Remove superfluous asserts
  With the QUIET log level now starting at 0, we no longer need to check
  for negative log levels.
diff: @@ -333,7 +333,6 @@ actor_id logger::thread_local_aid(actor_id aid) {
  }
  void logger::log(event&& x) {
  - CAF_ASSERT(x->level >= 0 && x->level <= 4);
  if (cfg_.inline_output)
  handle_event(x);
  else
  @@ -352,7 +351,6 @@ logger* logger::current_logger() {
  }
  bool logger::accepts(int level, string_view cname) {
  - CAF_ASSERT(level >= 0 && level <= 4);
  if (level > cfg_.verbosity)
  return false;
  if (!component_filter.empty()) {
  