Allow deletion of DNS routes via cloudflared command line tool💡

**Describe the feature you'd like**
There is already a feature in 32336859f82 to delete CIDR routes but not DNS routes. While the API can be used it would be more convenient to have this in cloudflared.

**Describe alternatives you've considered**
The API should allow this to happen but it'll be easier to do this in the cloudflared cli tool. [This issue requested the same](https://github.com/cloudflare/cloudflared/issues/328) but was closed. The [comment here](https://github.com/cloudflare/cloudflared/issues/328#issuecomment-808555111) misinterpreted the changelog; that changelog entry was not for DNS routes but, rather, network (CIDR netblocks) routes.

**Additional context**
This is useful for automated pipelines creating and deleting tunnels as part of CI/CD in service of developer testing.