Dependencies API: `DELETE`

Add `DELETE /api/v1/environments/{environment_api_key}/features/{feature}/dependencies/{prerequisite_feature}`.

`DELETE`:
- removes a correspodning rule.
- if the rule was the last one, removes the segment.

### Acceptance criteria

- `DELETE` removes the rule for a given prerequisite feature.
- `DELETE` removes the segment if the rule for a given prerequisite feature was the last one.
- `DELETE` for a dependency arising from a user-authored segment is refused with a 400.
- V2 versioning environments get a published version.
- V1 versioning environments get a direct write.
- Both V2 and V1 versioned environments emit audit logs.
- Requires `MANAGE_SEGMENT_OVERRIDES` on the environment.
- A caller who can not write on the environment gets 404.