message: Make linter happy
  Summary:
  Removing redundant `protected:`.
  This is a behavior-preserving change.
diff: @@ -222,7 +222,6 @@ class ConcurrentContainer {
  std::mutex& get_lock(size_t slot) const { return m_locks[slot]; }
  - protected:
  mutable std::mutex m_locks[n_slots];
  Container m_slots[n_slots];
  };
  