refactor(pipes): use angular lifecycle hooks instead of PipeOnDestroy

BREAKING CHANGE:
Previously, pipes that wanted to be notified when they were destroyed
would implement the PipeOnDestroy interface and name the callback
`onDestroy`. This change removes the PipeOnDestroy interface and
instead uses Angular's lifecycle interface `OnDestroy`, with the
`ngOnDestroy` method.

Before:
```
import {Pipe, PipeOnDestroy} from 'angular2/angular2';
@Pipe({pure: false})
export class MyPipe implements PipeOnDestroy {
  onDestroy() {}
}
```

After:
import {Pipe, OnDestroy} from 'angular2/angular2';
@Pipe({pure: false})
export class MyPipe implements PipeOnDestroy {
  ngOnDestroy() {}
}

modules/angular2/test/public_api_spec.ts

@@ -108,7 +108,7 @@ var NG_ALL = [
   'ApplicationRef.tick()',
   */
   'AsyncPipe',
-  'AsyncPipe.onDestroy()',
+  'AsyncPipe.ngOnDestroy()',
   'AsyncPipe.transform()',
   'Attribute',
   'Attribute.attributeName',
@@ -1425,7 +1425,6 @@ var NG_ALL = [
   'OnChanges:dart',
   'OnDestroy:dart',
   'OnInit:dart',
-  'PipeOnDestroy:dart',
   'PipeTransform:dart',
   'reflector',
   'RenderBeginCmd:dart',