Fix bugs in Material.remove_nuclide and Material.remove_element
Fix bugs in Material.remove_nuclide and Material.remove_element

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