removed unnecessary modification in cross_section.F90
removed unnecessary modification in cross_section.F90

mit-crpg/openmc,mit-crpg/openmc,liangjg/openmc,liangjg/openmc,mjlong/openmc,wbinventor/openmc,shikhar413/openmc,wbinventor/openmc,johnnyliu27/openmc,amandalund/openmc,paulromano/openmc,amandalund/openmc,walshjon/openmc,paulromano/openmc,paulromano/openmc,samuelshaner/openmc,bhermanmit/openmc,amandalund/openmc,johnnyliu27/openmc,smharper/openmc,liangjg/openmc,shikhar413/openmc,shikhar413/openmc,wbinventor/openmc,kellyrowland/openmc,mjlong/openmc,kellyrowland/openmc,mit-crpg/openmc,walshjon/openmc,bhermanmit/openmc,paulromano/openmc,smharper/openmc,samuelshaner/openmc,amandalund/openmc,liangjg/openmc,wbinventor/openmc,walshjon/openmc,smharper/openmc,mit-crpg/openmc,walshjon/openmc,johnnyliu27/openmc,shikhar413/openmc,smharper/openmc,samuelshaner/openmc,johnnyliu27/openmc,samuelshaner/openmc