Remove gemini mentions from conversational search guide and chat api ref

[CaroFG]

Pull Request

Related issue

Fixes #3465

What does this PR do?

• Remove gemini mentions from:
  • reference/api/chats.mdx
  • learn/chat/getting_started_with_chat.mdx

PR checklist

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• Did you use any AI tool while implementing this PR (code, tests, docs, etc.)? If yes, disclose it in the PR description and describe what it was used for. AI usage is allowed when it is disclosed.
• Does this PR fix an existing issue, or have you listed the changes applied in the PR description (and why they are needed)?
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• Have you made sure that the title is accurate and descriptive of the changes?

Thank you so much for contributing to Meilisearch!

[qdequele]

but, it was working before gemini.

[CaroFG]

but, it was working before gemini.

Not anymore...

[qdequele]

No in fact I found the test I did and it was the embeddings ! not the gemini llm.