docs(common): Remove async pipe from ngFor example (#33378)

Using the async pipe as the very first example makes it very confusing for beginners. Most people believe that | async is required for ngFor. I would remove that part to make the example solely focused on NgFor.
PR Close #33378

packages/common/src/directives/ng_for_of.ts

@@ -75,7 +75,7 @@ export class NgForOfContext<T> {
  * For example:
  *
  *  ```
- * <li *ngFor="let user of userObservable | async as users; index as i; first as isFirst">
+ * <li *ngFor="let user of users; index as i; first as isFirst">
  *    {{i}}/{{users.length}}. {{user}} <span *ngIf="isFirst">default</span>
  * </li>
  * ```