Build

stylix: clean up `fromOs` #750

Job	Run time
List packages	23s
docs on x86_64-darwin	1m 26s
palette-generator on x86_64-darwin	2m 39s
docs on x86_64-linux	29s
palette-generator on x86_64-linux	36s
testbed-gnome-dark on x86_64-linux	2m 32s
testbed-gnome-light on x86_64-linux	3m 44s
testbed-kde-dark on x86_64-linux	3m 58s
testbed-kde-light on x86_64-linux	4m 7s
	19m 54s

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