message: fix segment fault in c-api Example
  the result from wasm_extern_as_func was not marked as "own"
  `sum_func` was not owned by itself, delete it will cause a double free
diff: @@ -100,7 +100,6 @@ int main(int argc, const char* argv[]) {
  printf("Results of `sum`: %d\n", results_val[0].of.i32);
  - wasm_func_delete(sum_func);
  wasm_module_delete(module);
  wasm_extern_vec_delete(&exports);
  wasm_instance_delete(instance);
  