refactor(common): remove unused H2Stream stub #2215

Job	Run time
Verify hyper.h is up to date	52s
Check Style	14s
Test with Miri	1m 24s
Test C API (FFI)	27s
Check MSRV	27s
features	28s
udeps	45s
Test stable on ubuntu-latest	1m 58s
Test stable on windows-latest	3m 28s
Test stable on macOS-latest	1m 51s
Test beta on ubuntu-latest	2m 11s
Test beta on windows-latest	2m 55s
Test beta on macOS-latest	1m 36s
Test nightly on ubuntu-latest	2m 34s
Test nightly on windows-latest	3m 51s
Test nightly on macOS-latest	3m 6s
Check exposed types	22s
Build docs	36s
CI is green	3s
	29m 8s

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