[stdlib] New integers simplify generic code!

Author: Dave Abrahams

test/Prototypes/CollectionTransformers.swift

@@ -57,11 +57,11 @@ internal func _splitRandomAccessIndexRange<
 ) -> [Range<C.Index>] {
   let startIndex = range.lowerBound
   let endIndex = range.upperBound
-  let length = elements.distance(from: startIndex, to: endIndex).toIntMax()
+  let length = elements.distance(from: startIndex, to: endIndex)
   if length < 2 {
     return [range]
   }
-  let middle = elements.index(startIndex, offsetBy: C.IndexDistance(length / 2))
+  let middle = elements.index(startIndex, offsetBy: length / 2)
   return [startIndex ..< middle, middle ..< endIndex]
 }