Iframe is announced with the component's completion status when displayTitle is set #53

Subject of the issue

When a YouTube component has a displayTitle, its iframe is announced with the component's completion status, e.g. "Incomplete. Intro video", and "Completed. Intro video" once the video is complete.

Your environment

• adapt-youtube v3.3.6 (master), core v6.79.0
• Chrome, any screen reader

Steps to reproduce

1. Add a YouTube component with a displayTitle.
2. Inspect the iframe's accessible name (DevTools Accessibility pane), or navigate to it with a screen reader.

Expected behaviour

The iframe is named by the title text only: "Intro video".

Actual behaviour

The name is "Incomplete. Intro video". #48 points the iframe at the component heading with aria-labelledby="{{_id}}-heading". Core's heading.hbs includes the screen-reader completion description inside that element, so it becomes part of the iframe's name.