util/cmpx: remove code that's in the stdlib now

The cmpx.Compare function (and associated interface) are now available
in the standard library as cmp.Compare. Remove our version of it and use
the version from the standard library.

Updates #cleanup

Signed-off-by: Andrew Dunham <andrew@du.nham.ca>
Change-Id: I4be3ac63d466c05eb7a0babb25cb0d41816fbd53

util/cmpx/cmpx.go

@@ -20,40 +20,3 @@ func Or[T comparable](list ...T) T {
 	}
 	return zero
 }
-
-// Ordered is cmp.Ordered from Go 1.21.
-type Ordered interface {
-	~int | ~int8 | ~int16 | ~int32 | ~int64 |
-		~uint | ~uint8 | ~uint16 | ~uint32 | ~uint64 | ~uintptr |
-		~float32 | ~float64 |
-		~string
-}
-
-// Compare returns
-//
-//	-1 if x is less than y,
-//	 0 if x equals y,
-//	+1 if x is greater than y.
-//
-// For floating-point types, a NaN is considered less than any non-NaN,
-// a NaN is considered equal to a NaN, and -0.0 is equal to 0.0.
-func Compare[T Ordered](x, y T) int {
-	xNaN := isNaN(x)
-	yNaN := isNaN(y)
-	if xNaN && yNaN {
-		return 0
-	}
-	if xNaN || x < y {
-		return -1
-	}
-	if yNaN || x > y {
-		return +1
-	}
-	return 0
-}
-
-// isNaN reports whether x is a NaN without requiring the math package.
-// This will always return false if T is not floating-point.
-func isNaN[T Ordered](x T) bool {
-	return x != x
-}