removes destroy! method

The acts_as_archive gem defines a destroy! method that differs significantly from the rails 4 version. The method is intended to be used to destroy an object without archiving it. However, one of it's side effects is that it causes destroy callbacks to be skipped. Thus, calling destroy! on a user object will leave orphaned service and activation objects in the database, as the dependent => destroy hooks wouldn't run. Devs can easily get confused by this method since it exists in rails 4 without the negative side effects. Thus, I think the best option for us to avoid potential confusion is to simply remove the method from acts_as_archive.

Please note, the tests for acts_as_archive are broken on master, not just on my branch.