Drop Bind 9.8, 9.9 DLZ support -- too soon?

[Douglas Bagnall]

I wrote some patches that remove support for Bind versions < 9.10:

https://gitlab.com/samba-team/samba/-/merge_requests/1924

because the API changed, they went EOL years ago, and there are dozens of
lines of ifdefs that bring no pleasure to anyone.

But now I am having second thoughts. Things like RHEL7 are going to be
around for a while, and it seems like they might still have a Bind 9.9, at
least nominally.

In any case, please review the *first* patch there, which updates the
tests to use the new API.

Douglas