Revert "remove choices from validate_required"

This reverts commit 088fa96.

Author: RichDom2185

lib/cadet/assessments/question_types/mcq_question.ex

@@ -20,7 +20,7 @@ defmodule Cadet.Assessments.QuestionTypes.MCQQuestion do
     |> cast(params, @required_fields)
     |> cast_embed(:choices, with: &MCQChoice.changeset/2, required: true)
     |> validate_one_correct_answer
-    |> validate_required(@required_fields)
+    |> validate_required(@required_fields ++ ~w(choices)a)
   end
 
   defp validate_one_correct_answer(changeset) do