Revert of Oilpan: catch some self-referential leaks (main thread.)

Source/platform/heap/PersistentNode.h

Index: Source/platform/heap/PersistentNode.h
diff --git a/Source/platform/heap/PersistentNode.h b/Source/platform/heap/PersistentNode.h
index da8f3655f63fc72ca1d384fe2487d6b8f5a3ca56..338adf2b4ca7ba114ac580986d81928571d3d502 100644
--- a/Source/platform/heap/PersistentNode.h
+++ b/Source/platform/heap/PersistentNode.h
@@ -82,11 +82,6 @@
         return m_self;
     }
 
-    TraceCallback traceCallback() const
-    {
-        return m_trace;
-    }
-
 private:
     // If this PersistentNode is in use:
     //   - m_self points to the corresponding Persistent handle.
@@ -149,10 +144,6 @@
     void tracePersistentNodes(Visitor*);
     int numberOfPersistents();
 
-#ifndef NDEBUG
-    void dumpLivePersistents();
-#endif
-
 private:
     friend CrossThreadPersistentRegion;