Remove checked_sum impl for Weight

The `Weight` type does not use `NumOpResult<Weight>` with addition,
`Add` has `Output = Weight` and uses wrapping addition. This is as
expected and as desired. We do provide `Weight::checked_add` that
returns an `Option<Weight>`, also as expected and as desired.

Further context: `Amount` was deemed 'special' such that wrapping is
considered to big a risk to have silent wrapping so we added the
`NumOpResult` type. This argument does not apply to `Weight`.

We would like to remove the `CheckedSum` trait because summing of
`Amounts` can now be done with a combination of`Sum` and the
`NumOpResult` type but `Weight` currently implements `CheckedSum`.

For the reasons outline in regards to wrapping a `Weight` type,
providing `CheckedSum` does not add much value - remove it.

Done as preparation for removing the `CheckedSum` trait all together.

Author: tcharding

units/src/weight.rs

@@ -10,7 +10,7 @@ use arbitrary::{Arbitrary, Unstructured};
 #[cfg(feature = "serde")]
 use serde::{Deserialize, Deserializer, Serialize, Serializer};
 
-use crate::{Amount, CheckedSum, FeeRate, NumOpResult};
+use crate::{Amount, FeeRate, NumOpResult};
 
 /// The factor that non-witness serialization data is multiplied by during weight calculation.
 pub const WITNESS_SCALE_FACTOR: usize = 4;
@@ -251,13 +251,6 @@ impl ops::RemAssign<u64> for Weight {
     fn rem_assign(&mut self, rhs: u64) { *self = Weight::from_wu(self.to_wu() % rhs); }
 }
 
-impl<T> CheckedSum<Weight> for T
-where
-    T: Iterator<Item = Weight>,
-{
-    fn checked_sum(mut self) -> Option<Weight> { self.try_fold(Weight::ZERO, Weight::checked_add) }
-}
-
 impl core::iter::Sum for Weight {
     fn sum<I>(iter: I) -> Self
     where
@@ -541,16 +534,4 @@ mod tests {
         weight %= 3;
         assert_eq!(weight, Weight::from_wu(1));
     }
-
-    #[test]
-    #[cfg(feature = "alloc")]
-    fn checked_sum_weights() {
-        assert_eq!([].into_iter().checked_sum(), Some(Weight::ZERO));
-
-        let sum = alloc::vec![0, 1, 2].iter().map(|&w| Weight::from_wu(w)).checked_sum().unwrap();
-        assert_eq!(sum, Weight::from_wu(3));
-
-        let sum = alloc::vec![1, u64::MAX].iter().map(|&w| Weight::from_wu(w)).checked_sum();
-        assert!(sum.is_none());
-    }
 }