don't use unneeded closure

Co-authored-by: Alphyr <47725341+a1phyr@users.noreply.github.com>

library/core/src/iter/traits/iterator.rs

@@ -2608,7 +2608,7 @@ pub trait Iterator {
     /// assert_eq!(
     ///     vec![2.4, f32::NAN, 1.3]
     ///         .into_iter()
-    ///         .reduce(|a, b| f32::max(a, b))
+    ///         .reduce(f32::max)
     ///         .unwrap(),
     ///     2.4
     /// );