Disable old gitbooks docs website

[orville-wright]

No description provided.

[avishnu]

It's been decided to defer, since it's important to maintain the old release documentation contents for at least a year.

[edrob999]

Deferring is not a good option. The Gitbooks site still looks "live", and people may link to it.

Whata commonly done is an end of life notice on each page (for say 3 months), then remove the docs

Maintainers: please make a decision on the best course of action