TrigTruthEventTPCnv: 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.

Trigger/TrigTruthEvent/TrigTruthEventTPCnv/TrigTruthEventTPCnv/TrigIDHitStats_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
 */
 
 /**********************************************************************************
@@ -29,7 +29,7 @@ class TrigIDHitStats_p1
  public:
   
   TrigIDHitStats_p1() {}
-  virtual ~TrigIDHitStats_p1(){}
+  virtual ~TrigIDHitStats_p1() = default;
 
 
  private: