Never return chapters for audio content

[defagos]

Description

This PR removes (video) chapters which might still delivered for audio content, e.g. in Forum.

Changes made

Self-explanatory.

Checklist

• [x] APIs have been properly documented (if relevant).
• [x] The documentation has been updated (if relevant).
• [x] New unit tests have been written (if relevant).
• [x] The demo has been updated (if relevant).