Remove unnecessary constant declarations

The `controller` method already creates an anonymous class inheriting
from the class we pass it, so there's no need to create yet another
subclass.

spec/controllers/concerns/has_filters_spec.rb

@@ -1,9 +1,7 @@
 require "rails_helper"
 
 describe HasFilters do
-  class FakeController < ActionController::Base; end
-
-  controller(FakeController) do
+  controller(ActionController::Base) do
     include HasFilters
     has_filters ["all", "pending", "reviewed"], only: :index
 

spec/controllers/concerns/has_orders_spec.rb

@@ -1,9 +1,7 @@
 require "rails_helper"
 
 describe HasOrders do
-  class FakeController < ActionController::Base; end
-
-  controller(FakeController) do
+  controller(ActionController::Base) do
     include HasOrders
     has_orders ["created_at", "votes_count", "flags_count", "relevance"], only: :index
     has_orders ->(c) { ["votes_count", "flags_count"] }, only: :new