Adjust Equivalent trait

Note: It's a type inference break for the case of ``.remove(&&K)`` which
previously compiled (due to deref coercion?)

benches/bench.rs

@@ -557,7 +557,7 @@ fn remove_ordermap_100_000(b: &mut Bencher) {
     b.iter(|| {
         let mut map = map.clone();
         for key in &keys {
-            map.remove(&key).is_some();
+            map.remove(key).is_some();
         }
         assert_eq!(map.len(), 0);
         map

src/equivalent.rs

@@ -11,12 +11,12 @@ use std::borrow::Borrow;
 /// # Contract
 ///
 /// The implementor must hash like `K`, if applicable.
-pub trait Equivalent<K: ?Sized> {
+pub trait Equivalent<K> {
     /// Compare self to `key` and return `true` if they are equal.
     fn equivalent(&self, key: &K) -> bool;
 }
 
-impl<Q: ?Sized, K: ?Sized> Equivalent<K> for Q
+impl<Q: ?Sized, K> Equivalent<K> for Q
     where Q: Eq,
           K: Borrow<Q>,
 {

tests/equivalent_trait.rs

@@ -19,7 +19,7 @@ impl<A, B, C, D> PartialEq<(A, B)> for Pair<C, D>
     }
 }
 
-impl<A, B, X: ?Sized> Equivalent<X> for Pair<A, B>
+impl<A, B, X> Equivalent<X> for Pair<A, B>
     where Pair<A, B>: PartialEq<X>,
           A: Hash + Eq,
           B: Hash + Eq,