fix(upgrade): clean up scope when element is destroyed

Closes #8102

modules/angular2/src/upgrade/angular_js.ts

@@ -22,6 +22,7 @@ export interface IRootScopeService {
   $new(isolate?: boolean): IScope;
   $id: string;
   $watch(expr: any, fn?: (a1?: any, a2?: any) => void): Function;
+  $destroy(): any;
   $apply(): any;
   $apply(exp: string): any;
   $apply(exp: Function): any;

modules/angular2/src/upgrade/downgrade_ng2_adapter.ts

@@ -160,7 +160,10 @@ export class DowngradeNg2ComponentAdapter {
   }
 
   registerCleanup() {
-    this.element.bind('$destroy', () => this.viewManager.destroyRootHostView(this.hostViewRef));
+    this.element.bind('$destroy', () => {
+      this.componentScope.$destroy();
+      this.viewManager.destroyRootHostView(this.hostViewRef);
+    });
   }
 }