As of iOS8, when you delete a photo, it goes into a trashcan-analog called "Recently Deleted". This happens when you delete via Photos.app, or via the PhotoKit API (using PHAssetChangeRequest.deleteAssets()).
In Photos.app, you can then go into "Recently Deleted", and really delete that photo. Is there a way to do that in PhotoKit?
Nope. The only deletion API is deleteAssets.