Use delete instead of hiding copy constructors and assignments (#1820)

extras/tests/JsonSerializer/CustomWriter.cpp

@@ -8,6 +8,8 @@
 class CustomWriter {
  public:
   CustomWriter() {}
+  CustomWriter(const CustomWriter&) = delete;
+  CustomWriter& operator=(const CustomWriter&) = delete;
 
   size_t write(uint8_t c) {
     _str.append(1, static_cast<char>(c));
@@ -24,9 +26,6 @@ class CustomWriter {
   }
 
  private:
-  CustomWriter(const CustomWriter&);  // non-copiable
-  CustomWriter& operator=(const CustomWriter&);
-
   std::string _str;
 };