Merge branch 'HepMC3_Athena_Cleanup8_Comments' into 'master'

...idation/InDetPerformanceRTT/src/IDStandardPerformance.cxx

MuonSpectrometer/MuonTruthAlgs/src/MuonTrackTruthTool.cxx

...is/AnalysisCommon/EventUtils/src/ParticleCombinerTool.cxx

...ForwardDetectorsD3PDMaker/src/AlfaTruthInfoFillerTool.cxx

...3PDMaker/InDetD3PDMaker/src/SiHitTruthAssociationTool.cxx

...uthParticleID/McParticleTools/src/OldSpclMcFilterTool.cxx

Reconstruction/MET/METReconstruction/Root/METTruthTool.cxx

.../FastShower/FastCaloSim/src/FastShowerCellBuilderTool.cxx

...FastCaloSim/ISF_FastCaloSimServices/src/DNNCaloSimSvc.cxx

...CaloSim/ISF_FastCaloSimServices/src/FastCaloSimV2Tool.cxx

...lysisUtils/TrigInDetAnalysisUtils/Associator_TruthMatch.h

...stems/VP1TrackSystems/src/TrackCollHandle_TruthTracks.cxx