I believe that class is no longer used as of 4.2. Did you create this project as a code project or add code to a Blueprint project? Or did you build it from source? Either way, it is possible you added that file at some point and it shouldn’t be necessary anymore. Most likely it is referenced in [YourGame].h as an #include.
If you can find it and get rid of it, then build and save project, you should be able to convert project through Launcher to 4.3. Let me know if that doesn’t work or if you can’t find file.