Undo fix for change of dns class

```action operator
This release replaces the former (0.6.2) one. Please do not use
version 0.6.2, but this one instead.

0.6.2 contains an errornous fix for changing dns classes.
It will cause problems if two dns source controllers
are running with different dns-classes.
```

pkg/dns/source/dnsinfo.go

@@ -46,7 +46,7 @@ func (this *sourceReconciler) exclude(dns string) bool {
 
 func (this *sourceReconciler) getDNSInfo(logger logger.LogContext, obj resources.Object, s DNSSource, current *DNSCurrentState) (*DNSInfo, error) {
 	if !this.classes.IsResponsibleFor(logger, obj) {
-		return &DNSInfo{}, nil
+		return nil, nil
 	}
 	a := obj.GetAnnotations()[DNS_ANNOTATION]
 	current.AnnotatedNames = utils.StringSet{}