chore: remove gemini review

[huiwangredhat]

Summary

I received an email about Workflow Configuration Risks. I think it's time to remove the Gemini CLI review workflow. Here I listed two reasons:

• The Gemini CLI review is no longer meaningful. Because we now use the Claude code, the cursor helps us generate code. The real human review is more important than the Genini review at that stage.
• An outside collaborator with read-only access can trigger the workflow by
  opening a PR, causing:
  1. GCP Vertex AI API consumption (cost impact via secrets.GCP_SA_KEY)
  2. Secrets are not leaked to the collaborator, but the workflow runs on their behalf and consumes cloud resources.

[AlexXuan233]

LGTM

[marcusburghardt]

LGTM