chore: Remove unused region tags

[arbrown]

Description

Region tags have been migrated in documentation to new tags with the endpoints 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 3 region tags.

- [endpoints/getting-started/deployment.yaml:41](https://github.com/GoogleCloudPlatform/python-docs-samples/blob/ff2db976e5175817e4a8ea64044452a55282c9ca/endpoints/getting-started/deployment.yaml#L41), tag `esp` - [endpoints/kubernetes/k8s-grpc-bookstore.yaml:52](https://github.com/GoogleCloudPlatform/python-docs-samples/blob/ff2db976e5175817e4a8ea64044452a55282c9ca/endpoints/kubernetes/k8s-grpc-bookstore.yaml#L52), tag `service` - [endpoints/kubernetes/k8s-grpc-bookstore.yaml:68](https://github.com/GoogleCloudPlatform/python-docs-samples/blob/ff2db976e5175817e4a8ea64044452a55282c9ca/endpoints/kubernetes/k8s-grpc-bookstore.yaml#L68), tag `secret-2`

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