Use destroy_all instead of delete_all when deleting shipments

In Order#ensure_available_shipping_rates.
We should trigger ActiveRecord callbacks unless we have a good reason
not to.  In this case at least the `dependent: :delete_all` on
inventory units was being skipped.  This caused foreign key errors in
our app since we have foreign keys set up.

core/app/models/spree/order.rb

@@ -751,7 +751,7 @@ def ensure_available_shipping_rates
       if shipments.empty? || shipments.any? { |shipment| shipment.shipping_rates.blank? }
         # After this point, order redirects back to 'address' state and asks user to pick a proper address
         # Therefore, shipments are not necessary at this point.
-        shipments.delete_all
+        shipments.destroy_all
         errors.add(:base, Spree.t(:items_cannot_be_shipped)) and return false
       end
     end

core/spec/models/spree/order/checkout_spec.rb

@@ -597,6 +597,22 @@ def assert_state_changed(order, from, to)
         expect(order.reload.state).to eq 'payment'
       end
     end
+
+    context 'a shipment has no shipping rates' do
+      let(:order) { create(:order_with_line_items, state: 'confirm') }
+      let(:shipment) { order.shipments.first }
+
+      before do
+        shipment.shipping_rates.destroy_all
+      end
+
+      it 'clears the shipments and fails the transition' do
+        expect(order.complete).to eq(false)
+        expect(order.errors[:base]).to include(Spree.t(:items_cannot_be_shipped))
+        expect(order.shipments.count).to eq(0)
+        expect(Spree::InventoryUnit.where(shipment_id: shipment.id).count).to eq(0)
+      end
+    end
   end
 
   context "subclassed order" do