[Workers] Fix sample code in timers document

[nzws]

Summary

• Fix broken sample code in timers documentation.
• Tweak TypeScript types in the sample code.
• Remove unused code blocks.

Screenshots (optional)

Documentation checklist

• Is there a changelog entry (guidelines)? If you don't add one for something awesome and new (however small) — how will our customers find out? Changelogs are automatically posted to RSS feeds, the Discord, and X.
• The documentation style guide has been adhered to.
• If a larger change - such as adding a new page- an issue has been opened in relation to any incorrect or out of date information that this PR fixes.
• Files which have changed name or location have been allocated redirects.

[vicb]

Thanks for the update @nzws !

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