Revert "Adding link to prior versions of the docs."

Instead, add links to the web pages.

This reverts commit 87a5280b13f7092f730145028fcbdea8a8cc5519.

Conflicts:
	collects/scribblings/main/config.rkt
Add links to old documentations.

* The all-versions page has a docs column with html/pdf links, and also
  two links in the nightly builds footer.

* Specific version download pages have a link to the docs for that
  version.  (Only html, to save space.)