Drop wikinews wiki group

Closed last week, see [1] (but the Wikidata sitelinks still exist, at
least for now, see T425261). AFAICT, dropping it from the wiki groups is
enough to exclude it from the output.

[1]: https://meta.wikimedia.org/w/index.php?oldid=30328679#Board_of_Trustees_Approves_Closure_of_Wikinews

Bug: T425261