tools: remove xend and associated python modules

tools: remove xend and associated python modules

I've retained xen.lowlevel.{xc,xs} since they seem more widely useful. I also
kept xen.lowlevel.xl even though it is disabled by default and IMHO useless in
its current form.

I've tried to clean up the various associated bits like example configs, init
scripts, udev rules etc but no doubt I have missed something, those can easily
be cleaned up later.

I've also removed xm-test since although it could in theory be reworked to
test xl it hasn't been touched for years. If someone wants to resurrect it
then they could do so via the git history.

This has been built but not runtime tested.

Signed-off-by: Ian Campbell <ian.campbell@citrix.com>
---
v2: Clean out some .*ignore cruft
    Remove some xm/xend docs.