[BUG] Remove the deprecrated subscriber.dnsName

[Harwayne]

Describe the bug
subscriber.dnsName is a deprecated field.

Expected behavior
Remove the field in the release after the field is marked as deprecated (expected to be 0.5.0).

Related to #991.

[shashwathi]

/assign

[n3wscott]

Serving has not been deleting keys, we should not delete until v1beta1

[akashrv]

/priority important-longterm

[grantr]

Fixed by the switch to Destination.