Clear DescendantsTracker on each request.

activerecord/lib/active_record/railtie.rb

@@ -68,7 +68,6 @@ module ActiveRecord
       unless app.config.cache_classes
         ActiveSupport.on_load(:active_record) do
           ActionDispatch::Callbacks.after do
-            ActiveRecord::Base.reset_subclasses
             ActiveRecord::Base.clear_reloadable_connections!
           end
         end