* ros2pkg/resource/cpp/main.cpp.em: Use modern C++17 syntax. (#982)

Signed-off-by: 谢骐 <[email protected]>

Author: shynur

ros2pkg/ros2pkg/resource/cpp/main.cpp.em

@@ -1,10 +1,6 @@
 #include <cstdio>
 
-int main(int argc, char ** argv)
+int main([[maybe_unused]] int argc, [[maybe_unused]] char ** argv)
 {
-  (void) argc;
-  (void) argv;
-
   printf("hello world @(package_name) package\n");
-  return 0;
 }