Clean up CaloParticle interface in NeutralParticleMaker

The following discussion from !756 (merged) should be addressed:

• @sstahl started a discussion: (+2 comments)

  Do you know what CaloParticle is doing? The code here seems strange and it is kind of not obvious if it is actually doing anything. It looks like one should rather use functions instead of creating an object to manipulate the particle (if that is the case).

  Feel free to resolve this as an issue as this construct is not new, just that we do not forget.