Fix 8013 (#8027)

* Add @ngInject to HeatmapCtrl constructor, issue #8013

* Remove unused loadPluginCss

public/app/plugins/panel/heatmap/heatmap_ctrl.ts

@@ -99,6 +99,7 @@ export class HeatmapCtrl extends MetricsPanelCtrl {
   timeSrv: any;
   dataWarning: any;
 
+  /** @ngInject */
   constructor($scope, $injector, private $rootScope, timeSrv) {
     super($scope, $injector);
     this.$rootScope = $rootScope;

public/app/plugins/panel/heatmap/module.ts

@@ -1,6 +1,5 @@
 ///<reference path="../../../headers/common.d.ts" />
 
-import {loadPluginCss} from 'app/plugins/sdk';
 import {HeatmapCtrl} from './heatmap_ctrl';
 
 export {