Remove an unused header.

Removes the omnibox_popup_row.h header left for downstream compilation.

Bug: 814732
Cq-Include-Trybots: luci.chromium.try:ios-simulator-full-configs;master.tryserver.chromium.mac:ios-simulator-cronet
Change-Id: Ic7eb3c6f6d2b72496998ce58d7a81fc63614be69
Reviewed-on: https://chromium-review.googlesource.com/1158576Reviewed-by: Gauthier Ambard <gambard@chromium.org>
Commit-Queue: Stepan Khapugin <stkhapugin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#580112}

ios/chrome/browser/ui/omnibox/omnibox_popup_row.h

-// Copyright 2018 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.
-
-// TODO(crbug.com/814732): Remove this file once it's not included downstream.
-#import "ios/chrome/browser/ui/omnibox/popup/omnibox_popup_row.h"