Remove default hasher (#4739)

* remove default hasher from decl_storage!

* fix decl_storage declarations

substrate/frame/indices/src/lib.rs

@@ -108,7 +108,7 @@ decl_storage! {
 					].to_owned(),
 				))
 				.collect::<Vec<_>>()
-		}): map T::AccountIndex => Vec<T::AccountId>;
+		}): map hasher(blake2_256) T::AccountIndex => Vec<T::AccountId>;
 	}
 	add_extra_genesis {
 		config(ids): Vec<T::AccountId>;