chore(generative-ai): decommission obsolete count tokens advanced sample

[angelcaamal]

Description

Decommissions the count tokens advanced generative AI sample because it is no longer being used or updated. This updates the sample's metadata configuration to ensure it is hidden from the public sample browser.

This sample had this region tag:

• generativeaionvertexai_gemini_token_count_advanced

Fixes Internal: b/536061373

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 the countTokens sample implementation and its corresponding test file. There are no review comments, and I have no feedback to provide.

[Kef131]

Checked that files were not used in devsite, LGTM