Revert "resolved: address DVE-2018-0001"

Revert "resolved: address DVE-2018-0001"

DVE-2018-0001 has been fixed by the vendor, and this workaround is no longer
needed. Removal of this workaround improves performance as queries used to be
retried more than necessory.

This reverts 1ed4e584f3a03f47d2313314b6b5a78c9dc6f135.
This reverts https://github.com/systemd/systemd/pull/18638

Keep .clamp_feature_level_servfail name, as imho it is more descriptive than
just .clamp_feature_level, especially if we ever need to add similar
workarounds as the one we had for DVE-2018-0001.

However note that there is another retry which was added in
8a33aa199dc1cea14494469ac9d7d08dc6721df1 - seems to be working around Stubby
resolver behaviour.

Fixes: #26967