message: Remove obsolete comment and redundant prototype
diff: @@ -41,8 +41,6 @@ public:
  // A reference counted, implementation-specific implementation of a node ID.
  class data : public ref_counted {
  public:
  - // static intrusive_ptr<data> create_singleton();
  -
  ~data() override;
  virtual bool valid() const noexcept = 0;
  @@ -281,9 +279,6 @@ error inspect(serializer& sink, const node_id& x);
  /// @relates node_id
  error inspect(deserializer& source, node_id& x);
  -/// @relates node_id
  -std::string to_string(const node_id& x);
  -
  /// Appends `x` in human-readable string representation to `str`.
  /// @relates node_id
  void append_to_string(std::string& str, const node_id& x);
  