Fix really_destroy! for ruby 2.3

For some reason in ruby 2.3 this definition was interpreted as private.
There was no reason to be defining it where it was, so I've moved it
into the paranoia module.

lib/paranoia.rb

@@ -125,6 +125,30 @@ module Paranoia
   end
   alias :deleted? :paranoia_destroyed?
 
+  def really_destroy!
+    transaction do
+      run_callbacks(:real_destroy) do
+        dependent_reflections = self.class.reflections.select do |name, reflection|
+          reflection.options[:dependent] == :destroy
+        end
+        if dependent_reflections.any?
+          dependent_reflections.each do |name, reflection|
+            association_data = self.send(name)
+            # has_one association can return nil
+            # .paranoid? will work for both instances and classes
+            next unless association_data && association_data.paranoid?
+            if reflection.collection?
+              next association_data.with_deleted.each(&:really_destroy!)
+            end
+            association_data.really_destroy!
+          end
+        end
+        write_attribute(paranoia_column, current_time_from_proper_timezone)
+        destroy_without_paranoia
+      end
+    end
+  end
+
   private
 
   def paranoia_restore_attributes
@@ -185,31 +209,7 @@ class ActiveRecord::Base
   def self.acts_as_paranoid(options={})
     alias :really_destroyed? :destroyed?
     alias :really_delete :delete
-
     alias :destroy_without_paranoia :destroy
-    def really_destroy!
-      transaction do
-        run_callbacks(:real_destroy) do
-          dependent_reflections = self.class.reflections.select do |name, reflection|
-            reflection.options[:dependent] == :destroy
-          end
-          if dependent_reflections.any?
-            dependent_reflections.each do |name, reflection|
-              association_data = self.send(name)
-              # has_one association can return nil
-              # .paranoid? will work for both instances and classes
-              next unless association_data && association_data.paranoid?
-              if reflection.collection?
-                next association_data.with_deleted.each(&:really_destroy!)
-              end
-              association_data.really_destroy!
-            end
-          end
-          write_attribute(paranoia_column, current_time_from_proper_timezone)
-          destroy_without_paranoia
-        end
-      end
-    end
 
     include Paranoia
     class_attribute :paranoia_column, :paranoia_sentinel_value