gh-35731: build/pkgs/pyflakes: Remove

    
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### 📚 Description

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We remove this package; it is unused, and anyway all linters are
installed into tox environments.
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Resolves #30415
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### ⌛ Dependencies

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URL: #35731
Reported by: Matthias Köppe
Reviewer(s): Frédéric Chapoton