Merge pull request #12215 from ryantxu/use-ng-if-for-time

use ng-if for the panel timeInfo

public/app/features/panel/panel_header.ts

@@ -25,7 +25,7 @@ var template = `
       <li><a ng-click="ctrl.addDataQuery(datasource);"><i class="fa fa-trash"></i> Remove</a></li>
     </ul>
   </span>
-  <span class="panel-time-info" ng-show="ctrl.timeInfo"><i class="fa fa-clock-o"></i> {{ctrl.timeInfo}}</span>
+  <span class="panel-time-info" ng-if="ctrl.timeInfo"><i class="fa fa-clock-o"></i> {{ctrl.timeInfo}}</span>
 </span>`;
 
 function renderMenuItem(item, ctrl) {