We don't need to require AS::TestCase

This was only needed due to
6591a10b1f/railties/lib/rails/console_app.rb (L6)

We don't need that on master.

Fixes #6907.

railties/lib/rails/console/app.rb

@@ -1,9 +1,6 @@
 require 'active_support/all'
-require 'active_support/test_case'
 require 'action_controller'
 
-# work around the at_exit hook in test/unit, which kills IRB
-
 module Rails
   module ConsoleMethods
     # reference the global "app" instance, created on demand. To recreate the