Dropping libxml1

[Moritz Muehlenhoff <jmm@inutil.org>]

There are only three packages left, which build depend on libxml-dev
(r-cran-xml and cadaver have only alternate libxml2-dev | libxml-dev
 deps)

cheops-ng (#470011)
  -> gnome 1 only, low popcon, last maintainer upload from Feb 2007
amaterus (#470009)
  -> very low popcon (12), last maintainer upload from Jul 2004
koala (#470012)
  -> very low popcon (6), last maintainer upload from Auf 2005

None of the bugs have been followed up during the last month. Can
we move on and remove libxml1 and the three packages above out of
Lenny?

The maintainers of cheops-ng, amaterus and koala can still fix
their packages to use libxml2 before Lenny release to get them
back in.

Cheers,
        Moritz