Revert "Fix PoolStorage destructor"

This reverts commit 4c3d4c828e47d56eaaac38f6f835cc4447d82d60.

src/dgraph/pool.cpp

@@ -78,6 +78,7 @@ PoolStorage::
       dgDEBUG(15) << "Delete \""
 		   << (iter->first) <<"\""<<std::endl;
       Entity* entity = iter->second;
+      deregisterEntity(iter);
       delete (entity);
     }
   instance_ = 0;