Remove Question::Base#next_node_from_function_chain
Remove Question::Base#next_node_from_function_chain

As `@next_node_function_chain` is no longer set to anything other than
an empty array.

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