Remove must_use message

Co-authored-by: Jonas Böttiger <jonasboettiger@icloud.com>

Author: connortsui20

library/core/src/ops/range.rs

@@ -751,7 +751,7 @@ impl<T: Copy> Bound<&T> {
     /// assert_eq!((1..12).start_bound().copied(), Included(1));
     /// ```
     #[unstable(feature = "bound_copied", issue = "145966")]
-    #[must_use = "`self` will be dropped if the result is not used"]
+    #[must_use]
     pub fn copied(self) -> Bound<T> {
         match self {
             Bound::Unbounded => Bound::Unbounded,