remove useless setting

src/routes/Dashboard/Monitor.js

@@ -82,20 +82,6 @@ export default class Monitor extends PureComponent {
               bordered={false}
             >
               <Gauge
-                format={(val) => {
-                  switch (parseInt(val, 10)) {
-                    case 20:
-                      return '差';
-                    case 40:
-                      return '中';
-                    case 60:
-                      return '良';
-                    case 80:
-                      return '优';
-                    default:
-                      return '';
-                  }
-                }}
                 title="跳出率"
                 height={180}
                 percent={87}