Fix MediaSession action handler example

[coyaSONG]

Description

Clarifies the MediaSession play and pause action-handler example by selecting the page's <audio> element and removing calls to undefined demo-only status helpers. It also omits the unused catch binding in the same example.

Motivation

The current sample references audioEl, updateStatus, allMeta, and index without defining them, which makes the example difficult to understand or reuse. The updated example is focused on the documented media-session behavior and defines every value it uses.

Additional details

Validation completed:

• Prettier, Markdownlint, and CSpell on the changed page
• Repository test suite (5/5)
• JavaScript syntax and play/pause handler behavior checks
• Rari single-page build with no reported issues
• Repository pre-commit URL, cross-reference, front-matter, Prettier, and Markdownlint checks

Related issues and pull requests

Fixes #41250

[github-actions]

Preview URLs (1 page)

• /en-US/docs/Web/API/MediaSession