Remove elderly top level TODO file

The top level TODO file hasn't been touched since 2008, so it's now
an unhelpful and out of date mix of things that have already been done,
things that don't make sense any more and things which could in theory
be done but are not in practice important enough (or we'd have done
them some time in the last five years). Remove it. The bug tracking
system is probably a better place to track TODO items if we want to
do so.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Message-id: 1361377462-19816-1-git-send-email-peter.maydell@linaro.org
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>