去掉gridPanel表頭的全選框

給gridpanel 加上listener即可

,listeners:{
render:function(){
var hd_checker = this.getEl().select('p.x-grid3-hd-checker');
if (hd_checker.hasClass('x-grid3-hd-checker')) { 
     hd_checker.removeClass('x-grid3-hd-checker');
  }
}
}