crypto-common: remove `std` feature #1790

Job	Run time
build (1.81.0, thumbv7em-none-eabi)	14s
build (1.81.0, wasm32-unknown-unknown)	14s
build (stable, thumbv7em-none-eabi)	13s
build (stable, wasm32-unknown-unknown)	13s
test (1.81.0)	17s
test (stable)	18s
minimal-versions / minimal-versions	28s
	1m 57s

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