docs(router): Minor content update for Heroes tutorial

- Delete routerLinkActive from the earliest code example as it is not relevant to what the user is trying to achieve at that point in the tutorial

Author: massimocode

public/docs/_examples/toh-5/ts/app/app.component.ts

@@ -11,8 +11,8 @@ import { HeroService } from './hero.service';
   template: `
     <h1>{{title}}</h1>
     <nav>
-      <a [routerLink]="['/dashboard']" routerLinkActive="active">Dashboard</a>
-      <a [routerLink]="['/heroes']" routerLinkActive="active">Heroes</a>
+      <a [routerLink]="['/dashboard']">Dashboard</a>
+      <a [routerLink]="['/heroes']">Heroes</a>
     </nav>
     <router-outlet></router-outlet>
   `,