[#54594094] Refactor ResponsesController to initialise blank answers on `edit`.

- Instead of creating blank answers on `create`
- Also change ResponseDecorator to sort based on Survey#ordered_question_tree instead of Response#sorted_answers
[#54594094] Remove Response#sorted_answers and related methods.

- Not necessary anymore due to changes made in e246eb923eba87979e69381bb474fd29cb79f3a7