Remove Outcome#transition method
Remove Outcome#transition method

I don't think this method is serving much purpose. If the `transition` method is
called on an instance of `Outcome`, a `NoMethodError` exception will be raised
which should give just as much (if not more) information than this `InvalidNode`
exception.

alphagov/smart-answers,stwalsh/smart-answers,alphagov/smart-answers,aledelcueto/smart-answers,aledelcueto/smart-answers,alphagov/smart-answers,aledelcueto/smart-answers,stwalsh/smart-answers,stwalsh/smart-answers,stwalsh/smart-answers,aledelcueto/smart-answers,alphagov/smart-answers