Remove GenAI instrumentations that have never been released from this repo (#4903)

* Remove GenAI instrumentations that have never been released from this repo, point to opentelemetry-python-genai

* changelog

* lint

* stop auto-generating instrumentation-genai README

* Update instrumentation-genai/AGENTS.md

Co-authored-by: Aaron Abbott <aaronabbott@google.com>

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Co-authored-by: Aaron Abbott <aaronabbott@google.com>