fixup! Replace file_util.{h,cpp} by std::filesystem

Author: tautschnig

jbmc/unit/java-testing-utils/load_java_class.cpp

@@ -149,7 +149,7 @@ goto_modelt load_goto_model_from_java_class(
   // Log the working directory to help people identify the common error
   // of wrong working directory (should be the `unit` directory when running
   // the unit tests).
-  std::string path = std::filesystem::current_path();
+  std::string path = std::filesystem::current_path().string();
   INFO("Working directory: " << path);
 
   // if this fails it indicates the class was not loaded