resolver: fix duplicate removal from val_cname_new_signer to leave one copy
resolver: fix duplicate removal from val_cname_new_signer to leave one copy

pspacek and gdemidov managed to merge own version of duplicate record removal
at the same time, effectively removing both copies of the record.

This fix adds one copy back so the test has exactly one copy, as we
originally intended.

CZ-NIC/deckard,CZ-NIC/deckard