chore(grounding): remove decommissioned grounding samples

[angelcaamal]

Description

This PR removes the source code files and references for the following grounding code samples:

• generativeaionvertexai_grounding_private_data_basic
• generativeaionvertexai_grounding_public_data_basic

These samples are being deleted because their respective region tags are no longer used or required by Devsite. Cleaning them up helps reduce technical debt and avoids keeping unmaintained code in the repository.

Fixes Internal: b/533002326

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

Checklist

• I have followed guidelines from CONTRIBUTING.MD and Samples Style Guide
• Tests pass: npm test (see Testing)
• Lint pass: npm run lint (see Style)
• Required CI tests pass (see CI testing)
• 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 pull request is from a branch created directly off of GoogleCloudPlatform/nodejs-docs-samples. Not a fork.
• This sample adds a new sample directory, and I updated the CODEOWNERS file with the codeowners for this sample
• This sample adds a new sample directory, and I created GitHub Actions workflow 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

Note: Any check with (dev), (experimental), or (legacy) can be ignored and should not block your PR from merging (see CI testing).

[gemini-code-assist]

Code Review

This pull request removes two JavaScript sample files: one demonstrating content generation with Vertex AI Search grounding and another demonstrating content generation with Google Search grounding. I have no feedback to provide as there are no review comments.

[XrossFox]

Look good to me