Remove more branches from trainee journey

Removes the ineligiblity branches from the special case trainee teacher
journey. We want all eligibility checking to happen in one place (the
policy eligibility checker). This commit updates the mini trainee
journey to not check eligibility. This also surfaced a bug in the policy
eligiblity checker, a trainee teacher with an ineligible itt subject is
not yet ineligible, they may still be eligible later, we don't know
until they've entered their degree subject (at least according to the
logic in
`spec/features/trainee_teacher_subjourney_for_lup_schools_spec.rb:59`)

app/models/journeys/page_sequence.rb

@@ -20,12 +20,12 @@ def slugs
     end
 
     def next_slug
+      return "ineligible" if journey_ineligible?
+
       if lup_policy_and_trainee_teacher_at_lup_school?
         return handle_trainee_teacher
       end
 
-      return "ineligible" if journey_ineligible?
-
       if claim_submittable?
         return "student-loan-amount" if updating_personal_details? && in_sequence?("student-loan-amount")
         return "check-your-answers"
@@ -98,19 +98,15 @@ def lup_trainee_at_lup_school
     def handle_trainee_teacher
       case current_slug
       when "nqt-in-academic-year-after-itt"
-        @journey_session.answers.policy_year.in?(EligibilityCheckable::COMBINED_ECP_AND_LUP_POLICY_YEARS_BEFORE_FINAL_YEAR) ? "eligible-itt-subject" : "ineligible"
+        "eligible-itt-subject"
       when "eligible-itt-subject"
         if answers.eligible_itt_subject.to_sym.in? Policies::LevellingUpPremiumPayments.fixed_subject_symbols
           "future-eligibility"
         else
           "eligible-degree-subject"
         end
       when "eligible-degree-subject"
-        if @journey_session.answers.eligible_degree_subject?
-          "future-eligibility"
-        else
-          "ineligible"
-        end
+        "future-eligibility"
       end
     end
 

app/models/policies/levelling_up_premium_payments/policy_eligibility_checker.rb

@@ -74,11 +74,7 @@ def eligible_degree?
       end
 
       def specific_ineligible_attributes?
-        indicated_ecp_only_itt_subject? || trainee_teacher_with_ineligible_itt_subject? || ineligible_itt_subject_and_no_relevant_degree?
-      end
-
-      def trainee_teacher_with_ineligible_itt_subject?
-        trainee_teacher? && indicated_ineligible_itt_subject?
+        indicated_ecp_only_itt_subject? || ineligible_itt_subject_and_no_relevant_degree?
       end
 
       def ineligible_itt_subject_and_no_relevant_degree?