Use AtlasHepMC headers for updated CaloSamplingFractionAnalysis
In this MR:
- Use AtlasHepMC headers instead of HepMC directly.
- Switch to C++ range loop and a small fix to avoid null pointer deference ( production vertex).
Comment: It looks like this code was changed after the rest of the master switched to AtlasHepMC. That is why the first point is needed.