rdata: remove superfluous getters/setters

src/knot/dnssec/rrset-sign.c

src/knot/dnssec/zone-nsec.c

src/knot/events/handlers/parent_ds_query.c

src/knot/journal/serialization.c

src/knot/updates/ddns.c

src/knot/zone/contents.c

src/knot/zone/semantic-check.c

src/libknot/packet/rrset-wire.c

src/libknot/rdata.h

src/libknot/rdataset.c

src/libknot/rdataset.h

src/libknot/rrset-dump.c

src/libknot/rrset.c

src/libknot/rrtype/aaaa.c

src/libknot/rrtype/dnskey.h

src/libknot/rrtype/ds.c

src/libknot/rrtype/nsec.h

src/libknot/rrtype/nsec3.c

src/libknot/rrtype/opt.c

src/libknot/rrtype/rrsig.h