Homebrew 6 deprecations

[MikeMcQuaid]

The usual major release deprecation/disable/removal process.

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• Have you followed the guidelines in our Contributing document?
• Have you checked to ensure there aren't other open Pull Requests for the same change?
• Have you added an explanation of what your changes do and why you'd like us to include them? Performance claims (e.g. "this is faster") must include Hyperfine benchmarks.
• Have you written new tests (excluding integration tests) for your changes? Here's an example.
• Have you successfully run brew lgtm (style, typechecking and tests) with your changes locally?

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• AI was used to generate or assist with generating this PR.

Mostly done by hand, used OpenAI Codex 5.5 xhigh for some of the more tedious bits.

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