message: Remove unused member types
diff: @@ -35,8 +35,6 @@ namespace caf {
  class abstract_downstream {
  public:
  - using topics = std::vector<atom_value>;
  -
  using path = downstream_path;
  using path_cref = const path&;
  @@ -53,9 +51,6 @@ public:
  /// List of views to paths.
  using path_ptr_list = std::vector<path_ptr>;
  - /// Stores all available paths sorted by topics.
  - using path_map = std::unordered_map<topics, path_ptr_list>;
  -
  using policy_ptr = std::unique_ptr<downstream_policy>;
  abstract_downstream(local_actor* selfptr, const stream_id& sid,
  