changed 1e6 hardcoded number to hepmc sim increment

Philip Clarkrequested to merge
pclark/athena:mynewbranch into master

Removed hard coded 1000000 to use HepMC::SIM_REGENERATION_INCREMENT instead. This is to move away from using barcodes in a hardcoded fashion.

@averbyts @jchapman

Edited by Philip Clark

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