chore: Remove old region tag as part of migration

[arbrown]

Documentation updated to use new region tag with product prefix.

Checklist

• [x] I have followed Sample Guidelines from AUTHORING_GUIDE.MD
• [x] README is updated to include all relevant information
• [x] Tests pass: nox -s py-3.9 (see Test Environment Setup)
• [ ] Lint pass: nox -s lint (see Test Environment Setup)
• [ ] These samples need a new API enabled in testing projects to pass (let us know which ones)
• [ ] These samples need a new/updated env vars in testing projects set to pass (let us know which ones)
• [ ] This sample adds a new sample directory, and I updated the CODEOWNERS file with the codeowners for this sample
• [ ] This sample adds a new Product API, and I updated the Blunderbuss issue/PR auto-assigner with the codeowners for this sample
• [x] Please merge this PR for me once it is approved

[snippet-bot[bot]]

Here is the summary of changes.

You are about to delete 1 region tag.

- [compute/api/create_instance.py:166](https://github.com/GoogleCloudPlatform/python-docs-samples/blob/0a0803330c3575e8e54d42a08c0226db96f71d9b/compute/api/create_instance.py#L166), tag `wait_for_operation`

---

This comment is generated by snippet-bot. If you find problems with this result, please file an issue at: https://github.com/googleapis/repo-automation-bots/issues. To update this comment, add snippet-bot:force-run label or use the checkbox below:

• [ ] Refresh this comment

[gcf-merge-on-green[bot]]

Your PR has conflicts that you need to resolve before merge-on-green can automerge