Remove legacy InfoBarViewProtocol.

ios/chrome/browser/ui/infobars/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("infobars") {
   sources = [
     "infobar_view.h",
     "infobar_view.mm",
     "infobar_view_delegate.h",
-    "infobar_view_protocol.h",
   ]
   deps = [
     "//base",
     "//base:i18n",
     "//components/strings",
     "//ios/chrome/browser/ui",
     "//ios/chrome/browser/ui/colors",
     "//ios/chrome/browser/ui/fancy_ui",
     "//ios/chrome/browser/ui/infobars:resources",
     "//ios/chrome/browser/ui/util",
@@ skipping 58 matching lines @@
     "resources/infobar_update@2x.png",
     "resources/infobar_update@3x.png",
     "resources/infobar_warning.png",
     "resources/infobar_warning@2x.png",
     "resources/infobar_warning@3x.png",
   ]
   outputs = [
     "{{bundle_resources_dir}}/{{source_file_part}}",
   ]
 }