Remove dead code, this method was removed in spree 2.0.4

app/models/spree/shipment.rb

@@ -315,13 +315,5 @@ module Spree
     def update_order
       order.update!
     end
-
-    # NOTE: This is an override of spree's method, needed to allow orders
-    # without line items (ie. user invoices) to not have inventory units
-    def require_inventory
-      return false unless line_items.count > 0 # This line altered
-
-      order.completed? && !order.canceled?
-    end
   end
 end

spec/models/spree/shipment_spec.rb

@@ -339,7 +339,7 @@ describe Spree::Shipment do
   context "#ship" do
     before do
       order.stub(:update!)
-      shipment.stub(require_inventory: false, update_order: true, state: 'ready')
+      shipment.stub(update_order: true, state: 'ready')
       shipment.stub(adjustment: charge)
       shipping_method.stub(:create_adjustment)
       shipment.stub(:ensure_correct_adjustment)