Reframe LLM policy to be about quality, not tools

[yurishkuro]

A follow-up to #2417

My suggestion is to rewrite it without referencing LLMs. The overall guidance boils down to "don't create garbage/useless PRs", and "if you do we will block you". If a PR is high quality then it's irrelevant if it's created with GenAI help or not. We can expect most PRs to be done with AI assistance in the near future, so the guidance to "disclose that fact" serves no purpose.

[yurishkuro]

Closing as effectively a duplicate of #2434