Unbound host deletion returns null when criteria is met but host does not exist

Attempting to delete a Unbound host override that does not exist results in a null response:

```shell script
$ curl -k -X POST "https://172.16.209.129/api/v1/services/unbound/delete/hosts/?client-id=admin&client-token=pfsense&host=test&domain=jaredhendrickson.com"
null
```

The expected result is to return a response confirming the override does not exist