clean up exposed crate features #181

Job	Run time
Check Style	12s
features	39s
Test with Miri	41s
Check MSRV (1.63)	3m 52s
Test stable on ubuntu-latest	24s
Test stable on windows-latest	1m 29s
Test stable on macOS-latest	1m 10s
Test beta on ubuntu-latest	23s
Test beta on windows-latest	58s
Test beta on macOS-latest	54s
Test nightly on ubuntu-latest	22s
Test nightly on windows-latest	59s
Test nightly on macOS-latest	52s
Build docs	21s
CI is green	1s
	13m 17s

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