crypto-common: remove `std` feature #1792

Job	Run time
build (1.81.0, thumbv7em-none-eabi)	17s
build (1.81.0, wasm32-unknown-unknown)	20s
test (1.81.0)	17s
build (stable, thumbv7em-none-eabi)	10s
test (stable)	19s
build (stable, wasm32-unknown-unknown)	17s
minimal-versions / minimal-versions	32s
	2m 12s

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