libknot: remove KNOT_ERR_ALLOC_FAILED

src/knot/conf/conf.c

src/knot/dnssec/zone-keys.c

src/knot/dnssec/zone-sign.c

src/knot/updates/changesets.c

src/knot/zone/contents.c

src/knot/zone/node.c

src/knot/zone/semantic-check.c

src/knot/zone/zone-dump.c

src/knot/zone/zone.c

src/knot/zone/zonefile.c

src/libknot/common.h

src/libknot/rdataset.c

src/libknot/rrset.c

src/libknot/tsig-op.c