add a way to delete posts and topics when deleting a user with UserDestroyer

lib/user_destroyer.rb

@@ -11,10 +11,16 @@ class UserDestroyer
 
   # Returns false if the user failed to be deleted.
   # Returns a frozen instance of the User if the delete succeeded.
-  def destroy(user)
+  def destroy(user, opts={})
     raise Discourse::InvalidParameters.new('user is nil') unless user and user.is_a?(User)
-    raise PostsExistError if user.post_count != 0
+    raise PostsExistError if !opts[:delete_posts] && user.post_count != 0
     User.transaction do
+      if opts[:delete_posts]
+        user.posts.each do |post|
+          PostDestroyer.new(@admin, post).destroy
+        end
+        raise PostsExistError if user.reload.post_count != 0
+      end
       user.destroy.tap do |u|
         if u
           Post.with_deleted.where(user_id: user.id).update_all("nuked_user = true")