Fix the unused variable warnings:

./tensorflow/core/platform/default/protobuf.h:38:20: warning: 'tensorflow::kProtobufInt64Typename' defined but not used [-Wunused-variable]
 static const char* kProtobufInt64Typename = "::google::protobuf::int64";
                    ^
./tensorflow/core/platform/default/protobuf.h:39:20: warning: 'tensorflow::kProtobufUint64Typename' defined but not used [-Wunused-variable]
 static const char* kProtobufUint64Typename = "::google::protobuf::uint64";
Change: 133645400