MAINT: remove cell metadata `editable` and `slideshow` (#277) #440

Job	Run time
pytest / Determine job matrix	4s
style / Determine skipped pre-commit hooks	7s
doc / linkcheck / Check external links	38s
doc / nb / Execute and build documentation	2m 12s
pytest / Run unit tests (3.10, ubuntu-22.04)	1m 19s
pytest / Run unit tests (3.11, ubuntu-22.04)	1m 9s
pytest / Run unit tests (3.12, ubuntu-22.04)	1m 26s
pytest / Run unit tests (3.7, ubuntu-22.04)	1m 48s
pytest / Run unit tests (3.8, ubuntu-22.04)	1m 45s
pytest / Run unit tests (3.9, ubuntu-22.04, qrules)	4m 36s
pytest / Run unit tests (3.9, macos-12)	1m 30s
style / Run taplo through pre-commit	21s
style / Run local pre-commit hooks	51s
style / Push changes	0s
doc / Upload to GitHub Pages	0s
	17m 46s

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