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/core/linker/integration_spec.ts

@@ -54,7 +54,8 @@ import {
   Inject,
   Host,
   SkipSelf,
-  SkipSelfMetadata
+  SkipSelfMetadata,
+  OnDestroy
 } from 'angular2/core';
 
 import {NgIf, NgFor} from 'angular2/common';
@@ -1999,8 +2000,8 @@ class SomeViewport {
 }
 
 @Pipe({name: 'double'})
-class DoublePipe implements PipeTransform {
-  onDestroy() {}
+class DoublePipe implements PipeTransform, OnDestroy {
+  ngOnDestroy() {}
   transform(value, args = null) { return `${value}${value}`; }
 }