Get rid of old is_official_example machinery

[teh-cmc]

It conflicts with the new prefix-based way of doing things, leading to hashing stuff that shouldn't be hashed.

Checklist

• I have read and agree to Contributor Guide and the Code of Conduct
• I've included a screenshot or gif (if applicable)
• I have tested the web demo (if applicable):
  • Using newly built examples: app.rerun.io
  • Using examples from latest main build: app.rerun.io
  • Using full set of examples from nightly build: app.rerun.io
• The PR title and labels are set such as to maximize their usefulness for the next release's CHANGELOG
• If applicable, add a new check to the release checklist!

• PR Build Summary
• Docs preview
• Examples preview
• Recent benchmark results
• Wasm size tracking

[emilk]

Why is this marked as do-no-merge?

[teh-cmc]

Why is this marked as do-no-merge?

There are still tradeoffs to be decided upon, see https://rerunio.slack.com/archives/C033K5VS2KD/p1709741044889959

[teh-cmc]

It's just rotting at this point -- closing