Dynu test faiilures due to leftover TXT records

[tlhackque]

As noted in #691

The dynu failures seem to be because there are multiple TXT records - one of which is the expected record, but letsEncrypt is objecting to the others. See https://github.com/srvrco/getssl/runs/3235447284?check_suite_focus=true Probably a failure of a previous run to clean up.

The failures should clear up if you delete the TXT records. Might be a good idea for the first test to get and delete any TXT records for the test domains...

This can probably happen with the other dynamic domains- I just happened to run into it with dynu.

[timkimber]

Thanks for reporting this, I fixed this manually, but I'll add something to fix it automatically. I'll also check that it's not a bug somewhere in the tests

It can't occur for DuckDNS as that provider only allows a single TXT record for a domain.