StoreGateBindings: Remove DataBucketBase::clone().

DataBucketBase::clone() doesn't appear to be used anywhere.

Control/StoreGateBindings/src/SgPyDataModel.cxx

 /*
-  Copyright (C) 2002-2017 CERN for the benefit of the ATLAS collaboration
+  Copyright (C) 2002-2018 CERN for the benefit of the ATLAS collaboration
 */
 
 
@@ -145,16 +145,6 @@ namespace SG {
     return 0;
   }
 
-  PyDataBucket* PyDataBucket::clone() const
-  { 
-    PyErr_SetString
-      ( PyExc_RuntimeError, 
-	"SG::PyDataBucket::clone() is not meant to be called (yet)" );
-    std::abort();
-    return 0;
-//     new SG::PyDataBucket( m_type, copy<>(m_pyObj), m_clid );
-  }
-
   void PyDataBucket::lock()
   {
     RootUtils::PyGILStateEnsure gil;

Control/StoreGateBindings/src/SgPyDataModel.h

 // -*- C++ -*-
 
 /*
-  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 STOREGATEBINDINGS_SGPYDATAMODEL_H
@@ -147,12 +147,6 @@ namespace SG {
       return m_bib->typeinfo();
     }
 
-    /**
-     * @brief Return a new @c DataBucket whose payload has been cloned from the
-     *        original one.
-     */
-    virtual SG::PyDataBucket* clone() const override;
-
     /**
      * @brief Give up ownership of the  @c DataBucket contents.
      */