avoid ambiguous word

See rust-lang#113618 (review)

library/std/src/collections/hash/set.rs

@@ -66,7 +66,7 @@ use super::map::{map_try_reserve_error, RandomState};
 ///
 /// The easiest way to use `HashSet` with a custom type is to derive
 /// [`Eq`] and [`Hash`]. We must also derive [`PartialEq`],
-/// which is implied by [`Eq`].
+/// which is required if [`Eq`] is derived.
 ///
 /// ```
 /// use std::collections::HashSet;