Strange release note sources

[Martin Husemann <martin%duskware.de@localhost>]

Hey folks,

while working on release notes, I ran accross outdated xen information
(with lots of dead links) in src/distrib/notes/xen.

This directory seems to not be used for any of our release builds on
the auto-build cluster (or I am overlooking something) - so maybe we
should just remove it?

If not, please point out where it is used and update it to -current state!

Thanks,

Martin