Fix failing railties tests

A combination of two commits led into these failures:

* The addition of a new active_record config in
  24bb8347b6ff0da90059314d9aece7a2c94a272c
* The revert of the config to use config.x as options holder in
  43073b393d234acd094ac7c220163f4e419d11f5

These tests remove activerecord from the load path, however the
configuration is still in the application file, and they blow up.

railties/test/isolation/abstract_unit.rb

@@ -276,8 +276,12 @@ def controller(name, contents)
     end
 
     def use_frameworks(arr)
-      to_remove =  [:actionmailer,
-                    :activerecord] - arr
+      to_remove = [:actionmailer, :activerecord] - arr
+
+      if to_remove.include?(:activerecord)
+        remove_from_config 'config.active_record.*'
+      end
+
       $:.reject! {|path| path =~ %r'/(#{to_remove.join('|')})/' }
     end