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/Barcode/BarcodeInterfaces/BarcodeInterfaces/IBarcodeSvc.h

@@ -45,12 +45,6 @@ namespace Barcode {
     /** Generate a new unique vertex barcode below the simulation offset */
     virtual int newGeneratedVertex() = 0;
 
-    /** Generate a common barcode which will be shared by all children
-        of the given parent barcode (used for child particles which are
-        not stored in the mc truth event) */
-    virtual int sharedChildBarcode( int parentBC,
-                                                int process=0 ) = 0;
-
     /** Inform the BarcodeSvc about the largest particle and vertex Barcodes
         in the event input */
     virtual void registerLargestGeneratedParticleBC( int bc) = 0;