packet: removed RR merging as its deprecated

src/knot/ctl/remote.c

src/knot/nameserver/process_query.c

src/knot/server/rrl.c

src/knot/server/rrl.h

src/knot/server/xfr-handler.c

src/libknot/packet/pkt.c

src/libknot/packet/pkt.h

src/utils/dig/dig_exec.c

src/utils/nsupdate/nsupdate_exec.c