Stop setting use_qualified_include to true now that that is the default.

ios/chrome/app/strings/BUILD.gn

 # Copyright 2015 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("//build/config/locales.gni")
 import("//tools/grit/grit_rule.gni")
 
 group("strings") {
   public_deps = [
     ":ios_chromium_strings",
     ":ios_google_chrome_strings",
     ":ios_strings",
   ]
 }
 
 grit("ios_strings") {
   source = "ios_strings.grd"
   output_dir = "$root_gen_dir/ios/chrome"
-  use_qualified_include = true
   outputs = [
     "grit/ios_strings.h",
   ]
   foreach(locale, locales_with_fake_bidi) {
     outputs += [ "ios_strings_$locale.pak" ]
   }
 }
 
 grit("ios_chromium_strings") {
   source = "ios_chromium_strings.grd"
   output_dir = "$root_gen_dir/ios/chrome"
-  use_qualified_include = true
   outputs = [
     "grit/ios_chromium_strings.h",
   ]
   foreach(locale, locales_with_fake_bidi) {
     outputs += [ "ios_chromium_strings_$locale.pak" ]
   }
 }
 
 grit("ios_google_chrome_strings") {
   source = "ios_google_chrome_strings.grd"
   output_dir = "$root_gen_dir/ios/chrome"
-  use_qualified_include = true
   outputs = [
     "grit/ios_google_chrome_strings.h",
   ]
   foreach(locale, locales_with_fake_bidi) {
     outputs += [ "ios_google_chrome_strings_$locale.pak" ]
   }
 }