Update getEntryRecord

Andrii Verbytskyirequested to merge
averbyts/athena:hepmc3_nightly_fixes_05122020_part_2 into master

In this MR:

  • Update the getEntryRecord function fot HepMC3 compatibility
  • Use free functions from HepMC:: namespace
Edited by Andrii Verbytskyi

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