Those 3 wikis are unaccessible and unmaintained for years, and they are not supposed to contain anything that really worth keeping.
So I propose to simply get rid of them. I know we vaguely discussed backing them up, but it was a long time ago and nothing happened, if someone really wants to back them up then be my guest, but I don’t see the point of keep saying “we should back them up” and never do it.
The 3 wikis have been deleted today, as part of the upgrade.
For remaining links to enterprise.xwiki.org I opened Loading... and we are going to add redirection rules so that any old links to the old wiki is redirected to the main wiki.