chore: remove jsdom TextEncoder hack

[skyqrose]

Asana Task: None

I got a GitHub notification that the linked issue has just been resolved. jsdom has put out a new version with TextEncoder support. So we can remove our hack that was working around the missing feature.

Unfortunately we don't depend on jsdom directly, we'll have to wait for jest to update until we can use the new feature in jsdom. Until then, tests will fail.

This clearly isn't urgent or anything. But I wanted to open it while I'm thinking about it, and you can resolve it later whenever you happen to go through all the dependency updates in this repo.

Checklist

• Tests:
  • ( ) Has tests
  • ( ) Doesn't need tests
  • ( ) Tests deferred (with justification)
• Product/Design sign off:
  • ( ) Okayed the plan for the feature (e.g. the design files, or the Asana task)
  • ( ) Reviewed the feature as implemented (e.g. on dev-green, or saw screenshots)
  • (x) No review needed

[mathcolo]

Oops, I erroneously thought upgrading to jest v30 would contain jsdom >= 27.0.0, but it doesn't. Converting this to draft to avoid Slack notifications to review while we wait longer.