Drop dependency on futures-channel #3067

Job	Run time
Check Style	8s
semver	13s
Verify hyper.h is up to date	12s
Test C API (FFI)	30s
features	17s
Check MSRV	39s
Test stable on ubuntu-latest	21s
Test stable on windows-latest	33s
Test cargo-c support (FFI)	21s
Test beta on ubuntu-latest	28s
Test nightly on ubuntu-latest	32s
minimal-versions	37s
udeps	23s
Test beta on windows-latest	24s
Test nightly on macOS-latest	37s
Test stable on macOS-latest	29s
Test beta on macOS-latest	38s
Test nightly on windows-latest	29s
Test with Miri	46s
Check exposed types	0s
Build docs	0s
CI is green	0s
	8m 37s

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