jwjournal package files duplicated

- [x] I have read the [MiKTeX Contributing Guidelines](https://github.com/MiKTeX/miktex-packaging/blob/master/CONTRIBUTING.md)

The files `jwjournal-demo-cn.tex`, `jwjournal-demo-en.tex`, and `jwjournal-demo-fr.tex` of the [`jwjournal`](https://www.ctan.org/pkg/jwjournal) package are contained in both `.../source/jwjournal` and `doc/latex/jwjournal`.