Fix secondary photon creation
Fix secondary photon creation

This PR fixes #1472 .
I found that OpenMC counts the neutron weight twice when created secondary photons, once in the secondary photon weight and once in the number of photons produced.
The easiest way to fix this is just not counting the neutron weight Wn through the number of secondary photons when photons are generated.
paulromano/openmc,liangjg/openmc,paulromano/openmc,walshjon/openmc,walshjon/openmc,smharper/openmc,shikhar413/openmc,mit-crpg/openmc,liangjg/openmc,smharper/openmc,smharper/openmc,mit-crpg/openmc,paulromano/openmc,smharper/openmc,shikhar413/openmc,amandalund/openmc,amandalund/openmc,shikhar413/openmc,amandalund/openmc,mit-crpg/openmc,amandalund/openmc,shikhar413/openmc,paulromano/openmc,walshjon/openmc,mit-crpg/openmc,liangjg/openmc,liangjg/openmc,walshjon/openmc