Remove an unnecessary cast

Very minor thing, obviously, but I randomly saw this unnecessary cast showing up in the UbChecks, so might as well get rid of it.

library/core/src/num/uint_macros.rs

@@ -77,7 +77,7 @@ macro_rules! uint_impl {
                       without modifying the original"]
         #[inline(always)]
         pub const fn count_ones(self) -> u32 {
-            return intrinsics::ctpop(self as $ActualT);
+            return intrinsics::ctpop(self);
         }
 
         /// Returns the number of zeros in the binary representation of `self`.