chore(fixit): remove redundant region tags

[briandorsey]

Manually searched docs and confirmed no references remain. Only removed comments, no code changes.

Removed these tags:
run_helloworld_service
run_pubsub_handler

Description

Fixes #

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Checklist

• I have followed Sample Guidelines from AUTHORING_GUIDE.MD
• README is updated to include all relevant information
• 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
• Please merge this PR for me once it is approved

[snippet-bot]

Here is the summary of changes.

You are about to delete 2 region tags.

• run/helloworld/main.py:16, tag run_helloworld_service
• run/pubsub/main.py:27, tag run_pubsub_handler

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