There is a thread to add support for performing an unregistration from UPS (not from APNs) in the iOS SDK:

• http://lists.jboss.org/pipermail/aerogear-users/2016-April/000710.html

The RESTful API supports this:

• https://aerogear.org/docs/specs/aerogear-unifiedpush-rest/index.html#417932897

As well as the Android SDK:

• https://github.com/aerogear/aerogear-android-push/blob/master/aerogear-android-push/src/main/java/org/jboss/aerogear/android/unifiedpush/PushRegistrar.java#L40
  (but caution this also will remove from GCM)