Major WMDE work on wikidiff2 is finished for quite some time now, this testing tool was out of service for quite a while now and can be cleaned up.
https://toolsadmin.wikimedia.org/tools/id/wikidiff2-dev-test
See also:
T298875: Cleanup WMDE-TechWish tools
T305355: Upgrade/Delete TechWish tools that running on deprecated stretch grid