Removed unused variables in physics module.
Removed unused variables in physics module.

amandalund/openmc,smharper/openmc,mjlong/openmc,johnnyliu27/openmc,bhermanmit/openmc,wbinventor/openmc,wbinventor/openmc,mit-crpg/openmc,shikhar413/openmc,shikhar413/openmc,kellyrowland/openmc,nhorelik/openmc,bhermanmit/openmc,bhermanmit/cdash,lilulu/openmc,mit-crpg/openmc,johnnyliu27/openmc,kellyrowland/openmc,shenqicang/openmc,nhorelik/openmc,shenqicang/openmc,liangjg/openmc,shikhar413/openmc,walshjon/openmc,paulromano/openmc,walshjon/openmc,sxds/opemmc,mit-crpg/openmc,liangjg/openmc,wbinventor/openmc,walshjon/openmc,samuelshaner/openmc,paulromano/openmc,samuelshaner/openmc,shikhar413/openmc,paulromano/openmc,sxds/opemmc,smharper/openmc,walshjon/openmc,samuelshaner/openmc,mit-crpg/openmc,lilulu/openmc,smharper/openmc,wbinventor/openmc,liangjg/openmc,samuelshaner/openmc,johnnyliu27/openmc,mjlong/openmc,smharper/openmc,johnnyliu27/openmc,liangjg/openmc,lilulu/openmc,amandalund/openmc,amandalund/openmc,paulromano/openmc,amandalund/openmc