**Reason**: Obsolete (requires LQT), and has security flaws. Only one wiki using it in WikiApiary, and that wiki is on 1.16.x, so it wouldn't even affect them anyways.
- [x] Archive documentation on `mediawiki.org` (https://www.mediawiki.org/wiki/Extension:Reflect).
- [x] Remove from `mediawiki/extensions` (along with in `.gitmodules`).
- [ ] Remove tests in `integration/config` (`zuul/layout.yaml`).
- [x] Remove from `translatewiki` (`groups/MediaWiki/mediawiki-extensions.txt``).
- [x] Remove manifest/other references from `mediawiki/vagrant` if they exist.
- [x] Empty repository and add an ARCHIVED file.
- [x] Remove from https://doc.wikimedia.org/cover-extensions/ if present (requires #continuous-integration-infrastructure shell user to delete directly from the server)
- [x] Archive the extension's diffusion repository: https://phabricator.wikimedia.org/diffusion/EREF/
- [x] Mark the repository read-only in Gerrit: https://gerrit.wikimedia.org/g/mediawiki/extensions/Reflect
- [ ] Delete the GitHub mirror: https://github.com/wikimedia/mediawiki-extensions-Reflect