I would suggest to archive the unmaintained and inactive extension:
- [x] Archive documentation on `mediawiki.org` ( https://www.mediawiki.org/wiki/Extension:BookManagerv2 )
- [x] Remove from `mediawiki/extensions` ( along with in `.gitmodules`)
- [x] Remove tests in `integration/config` ( `zuul/layout.yaml` )
- [x] Remove from `translatewiki` ( `groups/MediaWiki/mediawiki-extensions.txt` )
- [x] Empty repository and add a ARCHIVED file.
- [x] Archive Phabricator project #MediaWiki-extensions-BookManagerv2 for associated extension
- [x] Edit Phabricator project #MediaWiki-extensions-BookManagerv2 description for associated extension with a link to this ticket
- [x] Archive the extension's diffusion repository: rEBMB
- [x] Mark the repository read-only in Gerrit: https://gerrit.wikimedia.org/r/#/admin/projects/mediawiki/extensions/BookManagerv2
- [ ] Delete the GitHub mirror: https://github.com/wikimedia/mediawiki-extensions-BookManagerv2