globalsystemfailure: Do not tangle our lists

If a globalsystemfailure happens, we must remove each query from its
corresponding list, since adns__query_fail will try to remove it and
then put it on some other list.

Previously, any globalsystemfailure was likely to lead to an assertion
failure.  This doesn't seem to me to be a security problem.

Found by AFL.

Signed-off-by: Ian Jackson <ijackson@chiark.greenend.org.uk>