knsupdate: fix delete operation

src/libknot/descriptor.c

src/libknot/rrset-dump.c

src/libknot/rrset-dump.h

src/utils/dig/dig_params.c

src/utils/host/host_params.c

src/utils/nsupdate/nsupdate_exec.c

src/utils/nsupdate/nsupdate_params.c