arpa: garbage collect ns_newmsg/ns_rdata decls

[val_packett.cool]

Summary

These were brought in by the libbind import in rG046c3635cd / rGe45764721a, but these functions were never actually implemented anywhere, only header declarations and symbol map entries were imported.

Reported by: ld.lld 16 being --no-undefined-version by default
Sponsored by: https://www.patreon.com/valpackett

[val_packett.cool]

include/arpa/nameser.h

558

or should they be #if 0'd like this?..