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

ios/chrome/browser/payments/cells/order_summary_line_item.mm

Index: ios/chrome/browser/payments/cells/order_summary_line_item.mm
diff --git a/ios/chrome/browser/payments/cells/order_summary_line_item.mm b/ios/chrome/browser/payments/cells/order_summary_line_item.mm
deleted file mode 100644
index 5bfadd0de0ca09d228a1325b4f5bfc66ccbe1d18..0000000000000000000000000000000000000000
--- a/ios/chrome/browser/payments/cells/order_summary_line_item.mm
+++ /dev/null
@@ -1,26 +0,0 @@
-// 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.
-
-#import "ios/chrome/browser/payments/cells/order_summary_line_item.h"
-
-#import "ios/third_party/material_components_ios/src/components/Palettes/src/MaterialPalettes.h"
-#import "ios/third_party/material_roboto_font_loader_ios/src/src/MaterialRobotoFontLoader.h"
-
-@implementation OrderSummaryLineItem
-
-#pragma mark CollectionViewItem
-
-- (void)configureCell:(CollectionViewDetailCell*)cell {
-  [super configureCell:cell];
-
-  cell.textLabel.font =
-      [[MDFRobotoFontLoader sharedInstance] regularFontOfSize:14];
-  cell.textLabel.textColor = [[MDCPalette greyPalette] tint900];
-
-  cell.detailTextLabel.font =
-      [[MDFRobotoFontLoader sharedInstance] regularFontOfSize:14];
-  cell.detailTextLabel.textColor = [[MDCPalette greyPalette] tint900];
-}
-
-@end