Update GRPO and RL diagrams

[melissawm]

Description

Update images.

Tests

N/A

Checklist

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• [N/A] I have performed a self-review of my code. For an optional AI review, add the gemini-review label.
• [N/A] I have necessary comments in my code, particularly in hard-to-understand areas.
• [N/A] I have run end-to-end tests tests and provided workload links above if applicable.
• I have made or will make corresponding changes to the doc if needed, including adding new documentation pages to the relevant Table of Contents (toctree directive) as explained in our documentation.

[bvandermoon]

LGTM, what was the issue with the original images?

[melissawm]

They had watermarks that are not useful in this repo (you can see them in the top and bottom right corners).