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() {}
}
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