StorageSvc: Fix gcc9 warnings.

In C++11, implicit declarations of copy and assignment are deprecated if the class has a user defined destructor or copy or assignment. gcc9 now warns about this by default. Adjust to avoid the warning.

Database/APR/StorageSvc/StorageSvc/DataCallBack.h

 /*
-  Copyright (C) 2002-2017 CERN for the benefit of the ATLAS collaboration
+  Copyright (C) 2002-2018 CERN for the benefit of the ATLAS collaboration
 */
 
 #ifndef POOL_DATACALLBACK_H
@@ -32,6 +32,10 @@ namespace pool {
     enum CallType  {  GET = 1, PUT = 2  };
     enum           {  SKIP = 3          };       // Flag to indicate skipping a column.
 
+    DataCallBack() = default;
+    DataCallBack(const DataCallBack&) = default;
+    DataCallBack& operator=(const DataCallBack&) = default;
+
     /// Standard destructor
     virtual ~DataCallBack()             {                                    }