Remove JSReceiver::GetPrototype and replace it with PrototypeIterator calls

src/objects.h

Index: src/objects.h
diff --git a/src/objects.h b/src/objects.h
index e13a90a89515d5ec03b0644b63d27fe669820320..b47bcb45d094db3b98cea9005de3f86d46f3d553 100644
--- a/src/objects.h
+++ b/src/objects.h
@@ -1989,9 +1989,6 @@ class JSReceiver: public HeapObject {
       Handle<JSReceiver> object,
       uint32_t index);
 
-  // Return the object's prototype (might be Heap::null_value()).
-  inline Object* GetPrototype() const;
-
   // Return the constructor function (may be Heap::null_value()).
   inline Object* GetConstructor();