remove duplicate validator::validateModel() method from io diagram
remove duplicate validator::validateModel() method from io diagram

hsorby/libcellml,libcellml/buildbot-testing,cellml/libcellml,nickerso/libcellml,hsorby/libcellml,cellml/libcellml,nickerso/libcellml,MichaelClerx/libcellml,nickerso/libcellml,cellml/libcellml,hsorby/libcellml,cellml/libcellml,hsorby/libcellml,MichaelClerx/libcellml,MichaelClerx/libcellml,nickerso/libcellml,libcellml/buildbot-testing