Remove references to https://drafts.csswg.org/biblio.ref

[JohnRiv]

Per w3c/csswg-drafts#11433, the file https://drafts.csswg.org/biblio.ref isn't used by anything any longer, and should be removed from that repo. Therefore, references to it in SpecRef should be removed.

The references to it are in refs/csswg.json & scripts/csswg.js. I think the best path forward is to move all the entries in refs/csswg.json to refs/biblio.json (there's only 1 item in refs/csswg.json with a different source, which I don't think impacts anything), and then delete scripts/csswg.js (and then by extension, also remove the reference to that script in scripts/run-all and also delete overwrites/csswg.json), but I want to make sure that's the best way before I put together a PR with all those changes.

[tidoust]

That seems a good path forward. Dropping refs/csswg.json is probably not fully necessary but that would at least signal that the information no longer comes from elsewhere.