Remove protobuf_mutator::String

It was use for compartibility with protobuf versions which use
absl::string. They are not relevant anymore.

Author: vitalybuka

port/protobuf.h

@@ -51,9 +51,6 @@ namespace protobuf_mutator {
 
 namespace protobuf = google::protobuf;
 
-// String type used by google::protobuf.
-using String = std::string;
-
 }  // namespace protobuf_mutator
 
 #endif  // PORT_PROTOBUF_H_

src/binary_format.cc

@@ -43,8 +43,8 @@ size_t SaveMessageAsBinary(const Message& message, uint8_t* data,
 }
 
 std::string SaveMessageAsBinary(const protobuf::Message& message) {
-  String tmp;
-  if (!message.SerializePartialToString(&tmp)) return {};
+  std::string tmp;
+  if (!message.SerializePartialToString(&tmp)) tmp.clear();
   return tmp;
 }
 

src/text_format.cc

@@ -49,8 +49,8 @@ size_t SaveMessageAsText(const Message& message, uint8_t* data,
 }
 
 std::string SaveMessageAsText(const protobuf::Message& message) {
-  String tmp;
-  if (!protobuf::TextFormat::PrintToString(message, &tmp)) return {};
+  std::string tmp;
+  if (!protobuf::TextFormat::PrintToString(message, &tmp)) tmp.clear();
   return tmp;
 }