Revert "Fix f64 examples"

This reverts commit 576426a05a.

src/libstd/f64.rs

@@ -971,17 +971,15 @@ impl f64 {
     }
 
     /// Returns max if self is greater than max, and min if self is less than min.
-    /// Otherwise this returns self.  Panics if min > max, min is NaN, or max is NaN.
+    /// Otherwise this returns self.  Panics if min > max, min equals NaN, or max equals NaN.
     ///
     /// # Examples
     ///
     /// ```
-    /// #![feature(clamp)]
-    /// use std::f64::NAN;
     /// assert!((-3.0f64).clamp(-2.0f64, 1.0f64) == -2.0f64);
     /// assert!((0.0f64).clamp(-2.0f64, 1.0f64) == 0.0f64);
     /// assert!((2.0f64).clamp(-2.0f64, 1.0f64) == 1.0f64);
-    /// assert!((NAN).clamp(-2.0f64, 1.0f64).is_nan());
+    /// assert!((NAN).clamp(-2.0f64, 1.0f64) == NAN);
     /// ```
     #[unstable(feature = "clamp", issue = "44095")]
     #[inline]