revert thread isolate in PreallocatedStorageAllocationPolicy

src/zone.h

Index: src/zone.h
diff --git a/src/zone.h b/src/zone.h
index 34fb7387eacce42d5e01a5ac7b470e33f8199ca1..bd7cc39b0c4f224b0646792fbd8ed262fdc5f986 100644
--- a/src/zone.h
+++ b/src/zone.h
@@ -174,11 +174,6 @@ struct ZoneScope {
 // structures to allocate themselves and their elements in the Zone.
 struct ZoneAllocationPolicy {
  public:
-  class Deleter {
-   public:
-    INLINE(explicit Deleter(const ZoneAllocationPolicy&)) {}
-    INLINE(static void Delete(void *pointer)) { }
-  };
   explicit ZoneAllocationPolicy(Zone* zone) : zone_(zone) { }
   INLINE(void* New(size_t size));
   INLINE(static void Delete(void *pointer)) { }