fix warning

readLib/source/Interface.dummy.cc

@@ -41,7 +41,7 @@ namespace corsika_data {
 
   // the fortran interface functions
   extern "C" {
-  void cordataopenfile_(const char* name, const int stringlength) {
+  void cordataopenfile_(const char* name, const int) {
     CorDataOpenFile(name);
   }
   void cordatafillarray_(double* data, const int& length) {