Remove old wikipedia leftovers
_The documentation is not available anymore as the PR was closed or merged._ > This makes me think we shouldn't advise the use of load_dataset in dataset scripts, since it doesn't guarantee that the cache will work as expected (the cache directory is not set correctly, and the required disk space for downloaded files is not recorded)

@lhoestq, do you think it could be a good idea to add a comment in this script WARNING that using load_dataset in a script is not good practice and that people should avoid using that script as a template to create other scripts?  good idea ! :)
After updating Wikipedia dataset, remove old wikipedia leftovers from doc.
