Integration: Align empty IO func on Windows

I think NullIO is fine on Windows now. We have it as an option in ctr
and it's used for the pod sandbox container in CRI. Lets see if CI agrees..

Signed-off-by: Danny Canter <danny@dcantah.dev>

integration/client/container_test.go

@@ -53,11 +53,6 @@ import (
 )
 
 func empty() cio.Creator {
-	// TODO (@mlaventure) windows searches for pipes
-	// when none are provided
-	if runtime.GOOS == "windows" {
-		return cio.NewCreator(cio.WithStdio, cio.WithTerminal)
-	}
 	return cio.NullIO
 }