message: core: drop 'operator << (ostream, String)' overload
  'cv::String' is 'std::string' in OpenCV 4.x
diff: @@ -73,12 +73,6 @@ public:
  typedef Vec<channel_type, channels> vec_type;
  };
  -static inline
  -std::ostream& operator << (std::ostream& os, const String& str)
  -{
  - return os << str.c_str();
  -}
  -
  static inline
  std::ostream& operator << (std::ostream& out, Ptr<Formatted> fmtd)
  {
  