faet: move mscharge derivation

app/models/derived_variables/sales_log_variables.rb

@@ -7,5 +7,8 @@ module DerivedVariables::SalesLogVariables
       self.exyear = exdate.year
     end
     self.deposit = value if outright_sale? && mortgage_not_used?
+    if mscharge_known.present? && mscharge_known.zero?
+      self.mscharge = 0
+    end
   end
 end

app/models/sales_log.rb

@@ -23,7 +23,6 @@ class SalesLog < Log
   before_validation :reset_invalidated_dependent_fields!
   before_validation :process_previous_postcode_changes!, if: :ppostcode_full_changed?
   before_validation :reset_previous_location_fields!, unless: :previous_postcode_known?
-  before_validation :process_mscharge_known_changes!, if: :mscharge_known_changed?
 
   scope :filter_by_year, ->(year) { where(saledate: Time.zone.local(year.to_i, 4, 1)...Time.zone.local(year.to_i + 1, 4, 1)) }
   scope :search_by, ->(param) { filter_by_id(param) }
@@ -152,10 +151,4 @@ class SalesLog < Log
   def mortgage_not_used?
     mortgageused == 2
   end
-
-  def process_mscharge_known_changes!
-    return if mscharge_known.blank?
-
-    self["mscharge"] = 0 if mscharge_known.zero?
-  end
 end