Don't "persist_amounts"

This association is autosaved, and Rails knows not to retouch things
when autosaving associated records. I did a test to confirm that
removing this doesn't change whether the field is persisted.

(cherry picked from commit 6106722)

Author: jarednorman

core/app/models/spree/in_memory_order_updater.rb

@@ -236,7 +236,6 @@ def recalculate_line_item_prices
     end
 
     def persist_totals
-      shipments.each(&:persist_amounts)
       log_state_change("payment")
       log_state_change("shipment")
       order.save!

core/spec/models/spree/in_memory_order_updater_spec.rb

@@ -575,7 +575,6 @@ module Spree
 
         it "updates the shipment amount" do
           expect(shipment).to receive(:assign_amounts)
-          expect(shipment).to receive(:persist_amounts)
           updater.recalculate
         end
       end