**Reason**: T195531
- [x] Archive documentation on [[http://mediawiki.org/wiki/Extension:NewUsersList|MediaWiki.org]]
- [x] Remove submodule from `mediawiki/extensions`
- [x] Remove tests in `integration/config`: `zuul/layout.yaml`
- [x] Remove from `translatewiki`: `groups/MediaWiki/mediawiki-extensions.txt`: https://gerrit.wikimedia.org/r/#/c/435126/
- [x] Remove manifest/other references from `mediawiki/vagrant` if they exist (not relevant here)
- [x] Empty repository and add a OBSOLETE file.
- [x] Archive Phabricator project #newuserslist
- [x] Edit Phabricator project #newuserslist description with a link to this ticket
- [x] Archive the extension's diffusion repository: https://phabricator.wikimedia.org/diffusion/ENUL/
- [x] Mark the repository read-only in Gerrit: https://gerrit.wikimedia.org/r/#/admin/projects/mediawiki/extensions/NewUsersList
- [x] Delete the GitHub mirror: https://github.com/wikimedia/mediawiki-extensions-NewUsersList