message: remove copy of shared_ptr in `remove_logger`
diff: @@ -594,7 +594,7 @@ public:
  void remove_logger(const Logger *logger) override
  {
  auto idx = find_if(begin(loggers_), end(loggers_),
  - [&logger](std::shared_ptr<const Logger> l) {
  + [&logger](std::shared_ptr<const Logger> &l) {
  return lend(l) == logger;
  });
  if (idx != end(loggers_)) {
  