Draft: Drop uses of HepMC
We are planning to switch from HepMC2 to HepMC3 in the upcoming LCG 106 (see SPI-2591).
HepMC3 is not backward compatible and it's very complicated to port LHCb code to it, so it was decided to drop the uses of it everywhere else then simulation code.
Part of a set: Phys!1088 Analysis!1055