[ng] template-syntax: drop *ngTrackFor examples (#327)

Fixes #303

Author: chalin

public/docs/_examples/template-syntax/dart/lib/app_component.html

@@ -616,18 +616,9 @@ <h4 id="ngFor-trackBy">NgForTrackBy</h4>
   <div *ngFor="let hero of heroes trackBy:trackByHeroes">({{hero.id}}) {{hero.fullName}}</div>
 </div>
 
-<p>with <i>*ngForTrackBy</i></p>
-<div class="box">
-  <!-- #docregion NgForTrackBy-2 -->
-  <div *ngFor="let hero of heroes" *ngForTrackBy="trackByHeroes">({{hero.id}}) {{hero.fullName}}</div>
-  <!-- #enddocregion NgForTrackBy-2 -->
-</div>
-
 <p>with <i>generic</i> trackById function</p>
 <div class="box">
-  <!-- #docregion NgForTrackBy-3 -->
-  <div *ngFor="let hero of heroes" *ngForTrackBy="trackById">({{hero.id}}) {{hero.fullName}}</div>
-  <!-- #enddocregion NgForTrackBy-3 -->
+  <div *ngFor="let hero of heroes, trackBy:trackById">({{hero.id}}) {{hero.fullName}}</div>
 </div>
 
 <a class="to-toc" href="#toc">top</a>

src/angular/guide/template-syntax.jade

@@ -1221,7 +1221,7 @@ figure.image-display
     Learn about other special *index-like* values such as `last`, `even`, and `odd` in the [NgFor API reference](/angular/api/angular2.common/NgFor-class.html).
 
 :marked
-  #### NgForTrackBy
+  #### NgFor *trackBy*
   The `ngFor` directive has the potential to perform poorly, especially with large lists.
   A small change to one item, an item removed, or an item added can trigger a cascade of DOM manipulations.
 
@@ -1236,7 +1236,7 @@ figure.image-display
   that two objects with the same `hero.id` are the same *hero*. Here is such a function:
 +makeExample('template-syntax/ts/app/app.component.ts', 'trackByHeroes')(format=".")
 :marked
-  Now set the `NgForTrackBy` directive to that *tracking* function.
+  We identify the tracking function using the ngFor `trackBy` option:
 +makeExample('template-syntax/ts/app/app.component.html', 'NgForTrackBy-2')(format=".")
 :marked
   The *tracking* function doesn't eliminate all DOM changes.