MAINT: remove cell metadata `editable` and `slideshow` #438

Job	Run time
pytest / Determine job matrix	6s
style / Determine skipped pre-commit hooks	6s
doc / nb / Execute and build documentation	30s
doc / linkcheck / Check external links	26s
pytest / Run unit tests (3.10, ubuntu-22.04)	8s
pytest / Run unit tests (3.11, ubuntu-22.04)	5s
pytest / Run unit tests (3.12, ubuntu-22.04)	3s
pytest / Run unit tests (3.7, ubuntu-22.04)	5s
pytest / Run unit tests (3.8, ubuntu-22.04)	2s
pytest / Run unit tests (3.9, ubuntu-22.04, qrules)	4s
pytest / Run unit tests (3.9, macos-12)	3s
style / Run local pre-commit hooks	9s
style / Run taplo through pre-commit	4s
style / Push changes	1s
doc / Upload to GitHub Pages	1s
	1m 53s

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