Inline trainee_teacher? method

This was the only method EligibilityCheckable was being pulled in for.
While we're duplicating the definition of a trainee teacher, inlining
the method here will make splitting up the EligibilityCheckable policy
easier.

app/forms/journeys/additional_payments_for_teaching/nqt_in_academic_year_after_itt_form.rb

@@ -1,8 +1,6 @@
 module Journeys
   module AdditionalPaymentsForTeaching
     class NqtInAcademicYearAfterIttForm < Form
-      include EligibilityCheckable
-
       attribute :nqt_in_academic_year_after_itt, :boolean
 
       validates :nqt_in_academic_year_after_itt, inclusion: {in: [true, false], message: i18n_error_message(:inclusion)}
@@ -23,6 +21,10 @@ def save
 
       private
 
+      def trainee_teacher?
+        nqt_in_academic_year_after_itt == false
+      end
+
       def determine_induction_answer_from_dqt_record
         return unless passed_details_check_with_teacher_id?
         # We can derive the induction_completed value for current_claim using the