[9.18] fix: usr: Remove unnecessary dns_name_free call

When processing a catalog zone member's primaries definition and
there is a TXT record containing an invalid name TSIG key name,
dns_name_free was incorrectly called triggering an assertion.
This has been fixed.

Closes #5858

Backport of MR !11832

Merge branch 'backport-5858-remove-unnecessary-dns-name-free-call-9.18' into 'bind-9.18'

See merge request isc-projects/bind9!11849