Remove various unused `std` feature deps. #82

Job	Run time
miri	1m 31s
build (ubuntu, stable, locked, true)	1h 11m 10s
build (windows, stable, locked, false)	31m 33s
build (macos, stable, locked, false)	23m 27s
build (ubuntu, nightly, locked, false)	16m 12s
build (ubuntu, beta, locked, false)	17m 10s
build (ubuntu, stable, latest, false)	26m 13s
build (ubuntu, stable, minimal, false)	18m 3s
fuzz	18m 9s
deploy	8s
	3h 43m 36s

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