The mediawiki.org interwiki prefix is required for various links in core (API docs etc.) and so should not be able to be deleted or changed from pointing to mediawiki.org (or at least should give a warning).

Some relevant discussions:
https://gerrit.wikimedia.org/r/c/mediawiki/core/+/169534/2/includes/api/i18n/en.json#9
https://gerrit.wikimedia.org/r/c/mediawiki/core/+/556102/2/languages/i18n/en.json#606