reuse GetIteratorDirect in GetIteratorFlattenable (#273)

spec.html

@@ -142,10 +142,7 @@ <h1>
         1. Else,
           1. Let _iterator_ be ? Call(_method_, _obj_).
         1. If _iterator_ is not an Object, throw a *TypeError* exception.
-        1. Let _nextMethod_ be ? Get(_iterator_, *"next"*).
-        1. If IsCallable(_nextMethod_) is *false*, throw a *TypeError* exception.
-        1. Let _iteratorRecord_ be the Iterator Record { [[Iterator]]: _iterator_, [[NextMethod]]: _nextMethod_, [[Done]]: *false* }.
-        1. Return _iteratorRecord_.
+        1. Return ? GetIteratorDirect(_iterator_).
       </emu-alg>
     </emu-clause>
   </emu-clause>