Remove io sample (#2490) #6168

Job	Run time
web/samples_index config check	43s
Test Flutter stable on ubuntu-latest	16m 33s
ios-build	6m 45s
Test Flutter stable on macos-latest	15m 22s
Test Flutter stable on windows-latest	25m 18s
Test Flutter beta on ubuntu-latest	10m 45s
Test Flutter beta on macos-latest	9m 39s
Test Flutter beta on windows-latest	17m 14s
Test Flutter master on ubuntu-latest	10m 30s
Test Flutter master on macos-latest	9m 52s
Test Flutter master on windows-latest	17m 6s
	2h 19m 47s

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