TrkEventTPCnv: 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.

Tracking/TrkEventCnv/TrkEventTPCnv/TrkEventTPCnv/VxVertex/Vertex_p1.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 VERTEX_P1_TRK_H
@@ -24,7 +24,7 @@ namespace Trk
   public:
   
     Vertex_p1() {}
-    virtual ~Vertex_p1() {}
+    virtual ~Vertex_p1() = default;
     
     std::vector<float>  m_position;