libknot: Removed redundant getters from rrset API.

src/knot/ctl/remote.c

src/knot/dnssec/zone-sign.c

src/knot/nameserver/internet.c

src/knot/updates/ddns.c

src/knot/zone/semantic-check.c

src/libknot/dnssec/rrset-sign.c

src/libknot/dnssec/sig0.c

src/libknot/edns.c

src/libknot/rdata/tsig.c

src/libknot/rrset-dump.c

src/libknot/rrset.c

src/libknot/rrset.h