Delete particles for Hijing HepMC2
Sometimes, Hijing produces particles with status 2 and without decay vertex. This is not appreciated by Geant4 who will throw an error; see ATLHI-483 or ATLMCPROD-11044. Merge request !65417 (merged) removes such particles if HEPMC3 is used. If that's not the case, the current code removes particles from the production vertex but it does not delete them, see the relevant HepMC code, which seems is not good enough for Geant. This MR deletes such particles completely.
Also adding a couple of print-outs in genInitialize, making the future debugging easier.