fix(go): remove gemini-3-pro-preview and claude-3-haiku@20240307

[andyma-star]

Summary

• Remove deprecated model references in Go plugins:
  • gemini-3-pro-preview (GoogleAI)
  • claude-3-haiku@20240307 (Vertex Model Garden)
• Update the affected Go sample and live test to use active model IDs without changing existing workflow logic.
• Keep docs aligned by removing deprecated model mention from the Go Google GenAI README.

Changes

• go/plugins/googlegenai/models.go
  • Filter out deprecated dynamically listed models (gemini-3-pro-preview).
• go/plugins/vertexai/modelgarden/models.go
  • Remove deprecated Anthropic model entry (claude-3-haiku@20240307).
• go/plugins/googlegenai/googleai_live_test.go
  • Replace deprecated model usage with gemini-2.5-pro.
• go/samples/multipart-tools/main.go
  • Replace deprecated model usage with googleai/gemini-2.5-pro.
• go/plugins/googlegenai/README.md
  • Remove deprecated Gemini model mention.

Issues

• Follows issue: https://github.com/invertase/genkit-private/issues/101

Checklist (if applicable):

• PR title is following https://www.conventionalcommits.org/en/v1.0.0/
• Tested (manually, unit tested, etc.)
• Docs updated (updated docs or a docs bug required)

[gemini-code-assist]

Code Review

This pull request deprecates the gemini-3-pro-preview model by updating documentation, tests, and samples to use gemini-2.5-pro, and implements a filtering mechanism for deprecated models in the Google AI plugin. Additionally, it removes the claude-3-haiku@20240307 model from the Vertex AI plugin. I have no feedback to provide.