Fix memory leak in cascade vertexing

Former-commit-id: 99a74283bc11c180527a58d0f28a595dcb0783dd

Tracking/TrkVertexFitter/TrkVKalVrtFitter/src/TrkCascadeFitter.cxx

@@ -747,7 +747,7 @@ VxCascadeInfo * TrkVKalVrtFitter::fitCascade(const Vertex* primVrt, bool FirstDe
        xaodVrtList.push_back(tmpXAODVertex);              //VK Save xAOD::Vertex
 //
 //---- Save and clean
-       delete tmpVTAV;delete tmpRecV;         //Mandatory cleaning
+       delete tmpVTAV;delete tmpRecV; delete fullDeriv;   //Mandatory cleaning
     }
 //
 //  Save momenta of all particles including combined at vertex positions