Remove custom deny_access handlers

Since these pages are not accessed by normal users, except for url fiddling, it's fine to respond with a generic access denied.

test/system/issues_test.rb

@@ -12,7 +12,7 @@ class IssuesTest < ApplicationSystemTestCase
     sign_in_as(create(:user))
 
     visit issues_path
-    assert page.has_content?(I18n.t("application.require_moderator_or_admin.not_a_moderator_or_admin"))
+    assert page.has_content?("Forbidden")
   end
 
   def test_view_no_issues