Remove uneeded PartialOrd bound in cmp::Ord::clamp

There is a Self: PartialOrd bound in Ord::clamp, but it is already
required by the trait itself. Likely a left-over from the const trait
deletion in 76dbe29104.

Reported-by: @noeensarguet

library/core/src/cmp.rs

@@ -901,7 +901,6 @@ fn min(self, other: Self) -> Self
     fn clamp(self, min: Self, max: Self) -> Self
     where
         Self: Sized,
-        Self: PartialOrd,
     {
         assert!(min <= max);
         if self < min {