remove unnecessary Default bound from Hash{Map,Set}'s Extend impl

Author: apasel422

src/libstd/collections/hash/map.rs

@@ -1508,7 +1508,7 @@ impl<K: Eq + Hash<S>, V, S, H: Hasher<S> + Default> FromIterator<(K, V)> for Has
 }
 
 #[stable]
-impl<K: Eq + Hash<S>, V, S, H: Hasher<S> + Default> Extend<(K, V)> for HashMap<K, V, H> {
+impl<K: Eq + Hash<S>, V, S, H: Hasher<S>> Extend<(K, V)> for HashMap<K, V, H> {
     fn extend<T: Iterator<Item=(K, V)>>(&mut self, mut iter: T) {
         for (k, v) in iter {
             self.insert(k, v);

src/libstd/collections/hash/set.rs

@@ -605,7 +605,7 @@ impl<T: Eq + Hash<S>, S, H: Hasher<S> + Default> FromIterator<T> for HashSet<T,
 }
 
 #[stable]
-impl<T: Eq + Hash<S>, S, H: Hasher<S> + Default> Extend<T> for HashSet<T, H> {
+impl<T: Eq + Hash<S>, S, H: Hasher<S>> Extend<T> for HashSet<T, H> {
     fn extend<I: Iterator<Item=T>>(&mut self, mut iter: I) {
         for k in iter {
             self.insert(k);