cubicweb #2502687 Remove XXX from published doc/book [deprecated]

Remove

[XXX ‘copy answer from forum’ means reusing text from http://groups.google.com/group/google-appengine/browse_frm/thread/c9476925f5f66ec6 and http://groups.google.com/group/google-appengine/browse_frm/thread/f48cf6099973aef5/c28cd6934dd72457 ]

from http://docs.cubicweb.org/annexes/faq.html

prioritynormal
typebug
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