MAINT: remove cell metadata `editable` and `slideshow` #437

Job	Run time
pytest / Determine job matrix	4s
style / Determine skipped pre-commit hooks	7s
doc / nb / Execute and build documentation	1m 12s
doc / linkcheck / Check external links	42s
style / Run local pre-commit hooks	42s
style / Run taplo through pre-commit	26s
pytest / Run unit tests (3.10, ubuntu-22.04)	1m 23s
pytest / Run unit tests (3.11, ubuntu-22.04)	1m 6s
pytest / Run unit tests (3.12, ubuntu-22.04)	1m 18s
pytest / Run unit tests (3.7, ubuntu-22.04)	1m 43s
pytest / Run unit tests (3.8, ubuntu-22.04)	1m 28s
pytest / Run unit tests (3.9, ubuntu-22.04, qrules)	4m 37s
pytest / Run unit tests (3.9, macos-12)	1m 37s
style / Push changes	0s
doc / Upload to GitHub Pages	0s
	16m 25s

Provide feedback