No CLI to unpublish a changelog note from a shipped bundle

### What happened?

Authors can publish a changelog note (`changelog note` + `changelog upload --artifact-type changelog`) and, if the release bundle already shipped, the scrubber adds it to `{parent}.amend-notes.yaml` so it appears in published docs.

There is no docs-builder command that reverses that. `changelog remove` only deletes local YAML and does not change published bundles or the CDN pool. `changelog upload` only writes objects (`PutObject`). `changelog bundle-amend --remove` writes a numbered sidecar, but if the note YAML is still in the pool the scrubber can treat it as a late note and put it back in `.amend-notes`.

Authors are not assumed to have S3 console access. Expected: an author who can upload can also take a note off a shipped release without hand-deleting bucket objects.

### How can we reproduce it?

1. Create and upload a `note-*.yml` after the product version’s bundle is already on the CDN (`changelog note`, then `changelog upload --artifact-type changelog`). Confirm the scrubber wrote `{parent}.amend-notes.yaml` and the note renders.
2. Run `changelog remove` on the local file (and/or `changelog bundle-amend --remove` + upload `amend-N`).
3. Observe: the pool object is still published; a later scrubber reconcile can restore the note via `.amend-notes`. There is no `changelog` subcommand whose documented effect is deleting `changelog/{org}/{repo}/{branch}/{file}` from the private bucket so the Lambda can drop the public copy.

### Version or commit

1.56.0+1da7c32f8561d7cbc1fc5ff1aa2dd52ebb34bb9c

Start by tracing the implementations of `changelog remove`, `changelog upload --artifact-type changelog`, and `changelog bundle-amend --remove`, then inspect the scrubber behavior described in the issue. Define the command's deletion effect for the private pool object and verify that a later reconcile cannot restore the removed note; add or run the relevant CLI and scrubber tests if they exist.

Written by the indexing model from the issue text.