Move max topup amount to policy

We'll be making topups availble on all polices so we don't want any
policy specific logic in the topup.

app/models/policies/levelling_up_premium_payments.rb

@@ -153,5 +153,9 @@ def selectable_itt_years_for_claim_year(claim_year)
     def closed?(claim_year)
       claim_year > POLICY_END_YEAR
     end
+
+    def max_topup_amount(claim)
+      Award.where(academic_year: claim.academic_year.to_s).maximum(:award_amount)
+    end
   end
 end

app/models/topup.rb

@@ -25,7 +25,8 @@ def teacher_reference_number
   def award_amount_must_be_in_range
     return unless award_amount.present?
 
-    max = Policies::LevellingUpPremiumPayments::Award.where(academic_year: claim.academic_year.to_s).maximum(:award_amount)
+    max = claim.policy.max_topup_amount(claim)
+
     total_amount = claim.award_amount_with_topups + award_amount
 
     unless total_amount.between?(1, max)