md4

Remove remaining uses of `doc(cfg(..))` #1022

Job	Run time
minimal-versions / minimal-versions	32s
set-msrv / set-msrv	3s
test (1.71.0)	25s
build (1.71.0, thumbv7em-none-eabi)	25s
test (stable)	35s
build (1.71.0, wasm32-unknown-unknown)	24s
build (stable, thumbv7em-none-eabi)	18s
build (stable, wasm32-unknown-unknown)	17s
	2m 59s

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