chore: remove stale notebooks/scripts, unlinked and years out of sync

[petercorke]

Summary

• notebooks/scripts/*.py was a one-off jupytext (py:light) export of the chapter notebooks from April 2022. Confirmed by regenerating the exact April-2022 notebook with jupytext and diffing against what was committed in that same commit — a near-exact structural match (unlike plain jupyter nbconvert --to python, which adds a shebang/coding header and # In[ ]: markers that these files never had).
• Only 4 of the 16 files were ever regenerated since (Jan 2023, "regenerated from book LaTeX source"). The rest — including chap2.py — have been frozen since the original commit while their source notebooks kept receiving fixes. Concretely: the framelabel/frame typo just fixed in chap2.ipynb (Fix frame labels in chapter 2 notebook #50) was still present in chap2.py.
• Nothing in the repo links to or documents this folder. notebooks/README.md's own "Convert to Python script" section already documents the manual jupyter nbconvert --to python command as the way to get a .py copy of a notebook, independent of whether one is pre-generated and committed.
• Removing the stale, undiscoverable copies rather than adding CI/bot machinery to keep them in sync — this repo has a light, book-companion maintenance model, and:
  • a CI drift-check would need a pinned jupytext dev-dependency (output format is version-sensitive — confirmed empirically) plus a required regenerate-before-commit step for every notebook edit, code or markdown;
  • an auto-commit bot can't actually work for external-contributor PRs (GitHub Actions' default token has no write access to a fork's branch), and even for direct pushes it removes the one human-review checkpoint on the generated diff.
• Also removes notebooks/Makefile, which only ever supported the reverse direction (.py → .ipynb via jupytext) and has no remaining purpose once the .py files it consumed are gone.

Test plan

• Grepped the whole repo (README, docs, notebooks, Makefile) for any reference to notebooks/scripts or notebooks/Makefile — none found
• Grepped tests/ for any reference to the removed files — none found
• Ran the fast test suite; two pre-existing failures encountered are unrelated environment gaps (missing nbformat, missing roboticstoolbox-python package metadata in this dev env), confirmed by reproducing them directly outside this change

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