when we click on insert variable button that time magentovariableplugin is not defined got this error so we added adminhtml_system_config_edit.xml and issue is resolved but system configuration layout has been changed why ? 
when we click on insert variable button that time magentovariableplugin is not defined got this error so we added adminhtml_system_config_edit.xml and issue is resolved but system configuration layout has been changed why ?