[BUG] Fix complete cleanup DNS Records

[slntopp]

Describe the bug

Deleting dns zone from Admin UI leaves an empty key. So i case there are two records

A *       10.0.0.0
A test  172.0.0.0

And we delete the test record from FE, it actually stays in the backend as test: {}. In such situation, attempts on resolving test. subdomain, will end up failed with no such host error

Front-end Used

• [X] Admin UI
• [ ] CLI
• [ ] Cloud App
• [ ] Other