### What problem does this PR solve?
Fixes a bug in the `rm_chunk` SDK interface where an `UnboundLocalError`
could
occur if `chunk_ids` is not provided in the request.
- `unique_chunk_ids` and `duplicate_messages` are now always initialized
in the `else` branch when `chunk_ids` is missing.
- API behavior remains unchanged when `chunk_ids` is present.
### Type of change
- [x] Bug Fix (non-breaking change which fixes an issue)