Removes two unnecessary cells + adds missing unit test for an existing cell

ios/chrome/browser/payments/cells/BUILD.gn

 # Copyright 2016 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 source_set("cells") {
   sources = [
-    "order_summary_line_item.h",
-    "order_summary_line_item.mm",
-    "order_summary_total_item.h",
-    "order_summary_total_item.mm",
     "page_info_item.h",
     "page_info_item.mm",
     "payment_method_item.h",
     "payment_method_item.mm",
     "shipping_address_item.h",
     "shipping_address_item.mm",
   ]
 
   deps = [
     "//ios/chrome/browser/ui/collection_view/cells",
     "//ios/third_party/material_components_ios",
     "//ios/third_party/material_roboto_font_loader_ios",
   ]
 
   configs += [ "//build/config/compiler:enable_arc" ]
 }
 
 source_set("unit_tests") {
   testonly = true
   sources = [
     "page_info_item_unittest.mm",
     "payment_method_item_unittest.mm",
+    "shipping_address_item_unittest.mm",
   ]
 
   deps = [
     ":cells",
     "//ios/chrome/browser/ui/collection_view/cells:test_support",
     "//ios/third_party/material_components_ios",
     "//testing/gtest",
   ]
 
   configs += [ "//build/config/compiler:enable_arc" ]
 }