TrkLinks: 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/TrkEvent/TrkLinks/TrkLinks/LinkToXAODNeutralParticle.h

 /*
-  Copyright (C) 2002-2017 CERN for the benefit of the ATLAS collaboration
+  Copyright (C) 2002-2019 CERN for the benefit of the ATLAS collaboration
 */
 
 #ifndef TRKTRACK_LINKTOXAODNEUTRALPARTICLE_H
@@ -38,7 +38,7 @@ namespace Trk
     LinkToXAODNeutralParticle( ElementLink<xAOD::NeutralParticleContainer>& link );
     
     /** default destructor */
-    virtual ~LinkToXAODNeutralParticle();
+    virtual ~LinkToXAODNeutralParticle() = default;
    
     /** dummy function to return 0 if TrackParameters are asked for */
     const TrackParameters* parameters() const { return NULL; };
@@ -49,9 +49,6 @@ namespace Trk
     /** method to clone the LinkToXAODNeutralParticle object */
     LinkToXAODNeutralParticle * clone() const ;
     
-    /** assignment operator */
-    Trk::LinkToXAODNeutralParticle& operator= ( const Trk::LinkToXAODNeutralParticle& rhs );
-   
     // This is here to make sure that the NeutralCollection typedef
     // will make it into the dictionary.
    // typedef NeutralCollection NeutralCollectionForDict;

Tracking/TrkEvent/TrkLinks/TrkLinks/LinkToXAODTrackParticle.h

 /*
-  Copyright (C) 2002-2017 CERN for the benefit of the ATLAS collaboration
+  Copyright (C) 2002-2019 CERN for the benefit of the ATLAS collaboration
 */
 
 #ifndef TRKTRACK_LINKTOXAODTRACKPARTICLE_H
@@ -38,9 +38,9 @@ namespace Trk
     
     /** constructor with ElementLink */
     LinkToXAODTrackParticle( ElementLink<xAOD::TrackParticleContainer>& link );
-    
+
     /** default destructor */
-    virtual ~LinkToXAODTrackParticle();
+    virtual ~LinkToXAODTrackParticle() = default;
    
     /** return the track parameters of the track (to which the EL< TrackCollection > points) */
     const TrackParameters* parameters() const;
@@ -51,9 +51,6 @@ namespace Trk
     /** method to clone the LinkToXAODTrackParticle object */
     LinkToXAODTrackParticle * clone() const ;
     
-    /** assignment operator */
-    Trk::LinkToXAODTrackParticle& operator= ( const Trk::LinkToXAODTrackParticle& rhs );
-   
     // This is here to make sure that the TrackCollection typedef
     // will make it into the dictionary.
    // typedef TrackCollection TrackCollectionForDict;

Tracking/TrkEvent/TrkLinks/src/LinkToXAODNeutralParticle.cxx

 /*
-  Copyright (C) 2002-2017 CERN for the benefit of the ATLAS collaboration
+  Copyright (C) 2002-2019 CERN for the benefit of the ATLAS collaboration
 */
 
 #include "TrkLinks/LinkToXAODNeutralParticle.h"
@@ -15,9 +15,6 @@ namespace Trk
 	LinkToXAODNeutralParticle::LinkToXAODNeutralParticle ( ElementLink<xAOD::NeutralParticleContainer>& link ) : ElementLink<xAOD::NeutralParticleContainer> ( link )
 	{}
 
-	LinkToXAODNeutralParticle::~LinkToXAODNeutralParticle()
-	{}
-
         const NeutralParameters* LinkToXAODNeutralParticle::neutralParameters() const
 	{
 		if ( isValid() )
@@ -34,12 +31,4 @@ namespace Trk
 		return new LinkToXAODNeutralParticle ( *this );
 	}
 
-	Trk::LinkToXAODNeutralParticle& Trk::LinkToXAODNeutralParticle::operator= ( const Trk::LinkToXAODNeutralParticle& rhs )
-	{
-		if ( this!=&rhs )
-		{
-			ElementLink<xAOD::NeutralParticleContainer>::operator= ( rhs );
-		}
-		return *this;
-	}
 }//end of namespace definitions

Tracking/TrkEvent/TrkLinks/src/LinkToXAODTrackParticle.cxx

 /*
-  Copyright (C) 2002-2017 CERN for the benefit of the ATLAS collaboration
+  Copyright (C) 2002-2019 CERN for the benefit of the ATLAS collaboration
 */
 
 #include "TrkLinks/LinkToXAODTrackParticle.h"
@@ -15,9 +15,6 @@ namespace Trk
 	LinkToXAODTrackParticle::LinkToXAODTrackParticle ( ElementLink<xAOD::TrackParticleContainer>& link ) : ElementLink<xAOD::TrackParticleContainer> ( link )
 	{}
 
-	LinkToXAODTrackParticle::~LinkToXAODTrackParticle()
-	{}
-
         const TrackParameters* LinkToXAODTrackParticle::parameters() const
 	{
 		if ( isValid() )
@@ -34,12 +31,4 @@ namespace Trk
 		return new LinkToXAODTrackParticle ( *this );
 	}
 
-	Trk::LinkToXAODTrackParticle& Trk::LinkToXAODTrackParticle::operator= ( const Trk::LinkToXAODTrackParticle& rhs )
-	{
-		if ( this!=&rhs )
-		{
-			ElementLink<xAOD::TrackParticleContainer>::operator= ( rhs );
-		}
-		return *this;
-	}
 }//end of namespace definitions