resolved: permit dnssec rrtype questions when we aren't validating

resolved: permit dnssec rrtype questions when we aren't validating

This check introduced in 91adc4db33f6 is intended to spare us from
encountering broken resolver behavior we don't want to deal with.
However if we aren't validating we more than likely don't know the state
of the upstream resolver's support for dnssec. Let's let clients try
these queries if they want.

This brings the behavior of sd-resolved in-line with previouly stated
change in the meaning of DNSSEC=no, which now means "don't validate"
rather than "don't validate, because the upstream resolver is declared to
be dnssec-unaware".

Fixes: 9c47b334445a ("resolved: enable DNS proxy mode if client wants DNSSEC")