Remove method that is not used on private model class.
Remove method that is not used on private model class.

MichaelClerx/libcellml,hsorby/libcellml,nickerso/libcellml,nickerso/libcellml,nickerso/libcellml,hsorby/libcellml,cellml/libcellml,MichaelClerx/libcellml,MichaelClerx/libcellml,hsorby/libcellml,cellml/libcellml,cellml/libcellml,cellml/libcellml,nickerso/libcellml,hsorby/libcellml