Add Spree::OrderCancellations#recalculate_adjustments

This removes the final occurrence of Spree::Adjustment#recalculate, and
makes it a cancellation-specific method. No checks for eligibility
(promotion only), no checks if it's taxed, very simple.

core/app/models/spree/order_cancellations.rb

@@ -96,6 +96,16 @@ def reimburse_units(inventory_units, created_by:)
     reimbursement
   end
 
+  def recalculate_adjustments
+    @order.line_items.each do |line_item|
+      line_item.adjustments.select(&:cancellation?).each do |adjustment|
+        next if adjustment.finalized?
+        amount = adjustment.source.compute_amount(line_item)
+        adjustment.update!(amount: amount)
+      end
+    end
+  end
+
   private
 
   def short_ship_unit(inventory_unit, created_by: nil)

core/app/models/spree/order_updater.rb

@@ -217,9 +217,7 @@ def update_taxes
     end
 
     def update_cancellations
-      line_items.each do |line_item|
-        line_item.adjustments.select(&:cancellation?).each(&:recalculate)
-      end
+      Spree::Config.order_cancellations_class.new(order).recalculate_adjustments
     end
 
     def update_item_totals