address review comments from leszko and j0sh

- Remove internal HTML docs (leszko/j0sh: not needed for internal cloud feature)
- Remove unused functions: enqueue_raw_event, update_api_key, report_event (leszko)
- Clarify SCOPE_CLOUD_API_KEY is user-provided and opt-in only (leszko)
- Add note that telemetry only fires for opted-in cloud users (leszko)

Signed-off-by: qianghan <qiang@livepeer.org>
Co-authored-by: Cursor <cursoragent@cursor.com>
Signed-off-by: qianghan <qiang@livepeer.org>

Author: seanhanca