Get rid of old web sites -- after insuring that content isn't lost

[masinter]

GitHub repo	served as
Interlisp/gitbook	docs.interlisp.org interlisp.gitbook.io
Interlisp/medley.wiki	github.om/Interlisp/medley/wiki
Interlisp/old.Interlisp.github.io	---

as noted with @neauoire PR

pls setup redirects so that old URLs get you something better than a 404