Drop unused concept of shared child particle barcodes

A long time ago, there was the idea that all child particles produced in a decay could be assigned the same barcode. This schema was never used and now we are migrating away from barcodes generally it seems like a good time to clean this unused code up.

• TruthSvc: Drop setSharedChildParticleBarcode method
• IBarcodeSvc + implementations: Drop sharedChildBarcode method
• ITruthIncident + implementations: Drop setAllChildrenBarcodes method
• ISFParticle: Drop unused setBarcodeAndUpdateHepMcParticleLink method (this was only called by ISFTruthIncident::setAllChildrenBarcodes)

Simulation/ISF/ISF_Core/ISF_Event/ISF_Event/ISFTruthIncident.h

@@ -96,8 +96,6 @@ namespace ISF {
         simulation) - TODO only a dummy implementation currently */
     virtual HepMC::GenParticlePtr     updateChildParticle(unsigned short index,
                                                           HepMC::GenParticlePtr existingChild) const override final;
-    /** Set the the barcode of all child particles to the given bc */
-    void                      setAllChildrenBarcodes(int bc) override final;
   private:
     ISFTruthIncident();