Remove an incorrect comment
It looks like this comment was copy-pasted from the previous doc test.
@@ -97,7 +97,6 @@ pin_project! {
/// let left = repeat(1);
/// let right = repeat(2);
///
-/// // We don't need any state, so let's make it an empty tuple.
/// let rrobin = |last: &mut PollNext| last.toggle();
///
/// let mut out = select_with_strategy(left, right, rrobin);
