refactor: remove pointless NXDOMAIN tests

test/255_dns_restart_test.sh

@@ -14,12 +14,10 @@ start_container          $HOST1 $C2/24 --name=c2 -h $NAME
 start_container_with_dns $HOST1 $C1/24 --name=c1
 
 assert_dns_record $HOST1 c1 $NAME $C2
-assert_raises "exec_on $HOST1 c1 dig MX $NAME | grep -q 'status: NXDOMAIN'"
 
 weave_on $HOST1 stop
 weave_on $HOST1 launch
 
 assert_dns_record $HOST1 c1 $NAME $C2
-assert_raises "exec_on $HOST1 c1 dig MX $NAME | grep -q 'status: NXDOMAIN'"
 
 end_suite

test/295_dns_large_response_test.sh

@@ -16,8 +16,6 @@ for i in $(seq $N); do
 done
 weave_on $HOST1 dns-add $IPS $CID -h $NAME
 
-assert_raises "exec_on $HOST1 c0 dig MX $NAME | grep -q 'status: NXDOMAIN'"
-
 check() {
     assert "exec_on $HOST1 c0 dig +short $* $NAME A | grep -v ';;' | wc -l" $N
 }