docs(toh-pt5/dart): remove an already existing line (#2056)

Remove an import statement as the package is already imported at this stage of the tutorial.

Author: benasocj

public/docs/dart/latest/tutorial/toh-pt5.jade

@@ -400,9 +400,9 @@ code-example(format='').
   We import the `HeroService`so we can fetch a hero.
 +makeExample('toh-5/dart/lib/hero_detail_component.dart', 'import-hero-service')(format=".")
 :marked
-  We import the `OnInit` interface because we'll call the `HeroService` inside the `ngOnInit` component lifecycle hook.
-+makeExample('toh-5/dart/lib/hero_detail_component.dart', 'import-oninit')(format=".")
-:marked
+  We use the `OnInit` interface from the already imported `angular2/core.dart` package because we'll
+  call the `HeroService` inside the `ngOnInit` component lifecycle hook.
+
   We inject both the `RouteParams` service and the `HeroService` into the constructor as we've done before,
   making private variables for both:
 +makeExample('toh-5/dart/lib/hero_detail_component.dart', 'ctor', 'lib/hero_detail_component.dart (constructor)')(format=".")