Remove dead code

Remove dead code

    *** CID 352817:  Control flow issues  (DEADCODE) /lib/ns/xfrout.c: 1568 in sendstream()
    1562
    1563     	/* Advance lasttsig to be the last TSIG generated */
    1564     	CHECK(dns_message_getquerytsig(msg, xfr->mctx, &xfr->lasttsig));
    1565
    1566     failure:
    1567     	if (msgname != NULL) {
    >>>     CID 352817:  Control flow issues  (DEADCODE)
    >>>     Execution cannot reach this statement: "if (msgrds != NULL) {
      if ...".
    1568     		if (msgrds != NULL) {
    1569     			if (dns_rdataset_isassociated(msgrds)) {
    1570     				dns_rdataset_disassociate(msgrds);
    1571     			}
    1572     			dns_message_puttemprdataset(msg, &msgrds);
    1573     		}