Fix duplicate message output in json-ui

Author: peterschrammel

src/util/ui_message.cpp

@@ -294,11 +294,6 @@ void ui_message_handlert::json_ui_msg(
   const std::string timestamp = time->stamp();
   if(!timestamp.empty())
     result["timestamp"] = json_stringt(timestamp);
-
-  // By convention a leading comma is created by every new array entry.
-  // The first entry is generated in the constructor and does not have
-  //  a trailing comma.
-  std::cout << ",\n" << result;
 }
 
 void ui_message_handlert::flush(unsigned level)