Hepmc3 nightly fixes 25112020 part 4

In this MR:

• use auto to assure HEpMC3 compatibility and avoid long type names
• use methods of STL containders for the case of HepMC3, e.g. particles().size() instead of particles_size().

PhysicsAnalysis/AnalysisCommon/UserAnalysis/src/AnalysisSkeleton.cxx

@@ -1306,14 +1306,14 @@ StatusCode AnalysisSkeleton::getTopQpT(int& numTops, double& top1, double& top2)
   numTops=0;
   for (; mcpItr != mcpItrE; ++mcpItr) {
 
-    const HepMC::GenParticle* part =(*mcpItr)->genParticle();
+    auto part =(*mcpItr)->genParticle();
     int pdgid = part->pdg_id();
 
     if(numTops==2) break; // quit if we have two already
 
     if(abs(pdgid)==6) { // it is a top
 
-      HepMC::GenVertex* prod_vtx = part->production_vertex();
+      auto prod_vtx = part->production_vertex();
       int vtx_barcode = 1;
       if(prod_vtx) vtx_barcode = HepMC::barcode(prod_vtx);