Remove an unused typedef.

Source/platform/heap/HeapTest.cpp

 /*
  * Copyright (C) 2013 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 4425 matching lines @@
 
     key.clear();
     Heap::collectGarbage(ThreadState::NoHeapPointersOnStack);
     EXPECT_EQ(0u, chain->map().size());
 }
 
 TEST(HeapTest, Ephemeron)
 {
     typedef HeapHashMap<WeakMember<IntWrapper>, PairWithWeakHandling>  WeakPairMap;
     typedef HeapHashMap<PairWithWeakHandling, WeakMember<IntWrapper> >  PairWeakMap;
-    typedef HeapHashMap<PairWithWeakHandling, PairWithWeakHandling>  PairPairMap;
     typedef HeapHashSet<WeakMember<IntWrapper> > Set;
 
     Persistent<WeakPairMap> weakPairMap = new WeakPairMap();
     Persistent<WeakPairMap> weakPairMap2 = new WeakPairMap();
     Persistent<WeakPairMap> weakPairMap3 = new WeakPairMap();
     Persistent<WeakPairMap> weakPairMap4 = new WeakPairMap();
 
     Persistent<PairWeakMap> pairWeakMap = new PairWeakMap();
     Persistent<PairWeakMap> pairWeakMap2 = new PairWeakMap();
 
@@ skipping 517 matching lines @@
 
     static volatile IntWrapper* s_workerObjectPointer;
 };
 
 TEST(HeapTest, RecursiveMutex)
 {
     RecursiveLockingTester::test();
 }
 
 } // WebCore namespace