chore: Remove deprecated Cloud Debugger sample

[mctavish]

Remove deprecated Cloud Debugger sample

Fixes #10237

Note: Before submitting a pull request, please open an issue for discussion if you are not associated with Google.

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.

• appengine/standard_python3/cloud_debugger/main.py:15, tag gae_python38_app
• appengine/standard_python3/cloud_debugger/main.py:16, tag gae_python3_app

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[leahecole]

I can see in devrel/ that this region tag isn't used in docs, and the region tag is actually duplicated elsewhere, so this fixes that as an added bonus. LGTM