tests: move test/helpers to test/test_helpers.

The Rails convention is for test/helpers to be used for testing the view
helpers in app/helpers. We were using it to store certain utility
methods instead. Move these to test/test_helpers so that test/helpers
can be used for its intended purpose.

test/functional/pool_versions_controller_test.rb

@@ -1,9 +1,6 @@
 require 'test_helper'
-require 'helpers/pool_archive_test_helper'
 
 class PoolVersionsControllerTest < ActionController::TestCase
-  include PoolArchiveTestHelper
-
   context "The pool versions controller" do
     setup do
       mock_pool_archive_service!