remove useless ivar clearing

Since we only work with new instances, these ivars will not be set.

actionpack/lib/action_controller/test_case.rb

@@ -101,12 +101,6 @@ def assign_parameters(routes, controller_path, action, parameters = {})
       path_parameters[:action] = action
 
       self.path_parameters = path_parameters
-
-      # Clear the combined params hash in case it was already referenced.
-      @env.delete("action_dispatch.request.parameters")
-
-      # Clear the filter cache variables so they're not stale
-      @filtered_parameters = @filtered_env = @filtered_path = nil
     end
 
     ENCODER = Class.new do