Don't delete Report when associated User is deleted

Right now, if a user reports a subject, then that user is deleted, the report is deleted but the subject remains blocked.

That seems strange to me, if the subject is still blocked then the report should probably continue to exist.

This implements that.

Even if this feature is going to be rejected, I would still like some feedback on the code, as this is my first attempt at writing my own core code after only writing tests so far. :)