stex package files duplicated

- [x] I have read the [MiKTeX Contributing Guidelines](https://github.com/MiKTeX/miktex-packaging/blob/master/CONTRIBUTING.md)

There is an unnecessary folder `.../MiKTeX/source/stex/source/stex` containing outdated versions of the files `stex.sty` and `stex.cls`, as well as a file `stex.log`.

Possibly related to #332.