Removed knot_rrset_(set_)ttl, use per-RR TTLs instead.

src/knot/dnssec/zone-sign.c

src/knot/nameserver/internet.c

src/knot/updates/ddns.c

src/knot/updates/xfr-in.c

src/knot/zone/semantic-check.c

src/knot/zone/zone-diff.c

src/libknot/dnssec/rrset-sign.c

src/libknot/rrset.c

src/libknot/rrset.h

src/libknot/tsig-op.c