uucore: remove div_ceil() from sum feature

src/uucore/src/lib/features/sum.rs

@@ -207,13 +207,6 @@ impl Digest for CRC {
     }
 }
 
-// This can be replaced with usize::div_ceil once it is stabilized.
-// This implementation approach is optimized for when `b` is a constant,
-// particularly a power of two.
-pub fn div_ceil(a: usize, b: usize) -> usize {
-    (a + b - 1) / b
-}
-
 pub struct BSD {
     state: u16,
 }