More cleanup of GYP code in ui/ozone

GYP files for Ozone have been removed in
https://codereview.chromium.org/2306743002

We remove some comments from the GN files referring to these GYP files.
We also remove the file ui/ozone/empty.cc, which is not used anymore.

R=rjkroege@chromium.org
BUG=none

Review-Url: https://codereview.chromium.org/2312763002
Cr-Commit-Position: refs/heads/master@{#416871}
diff --git a/ui/ozone/BUILD.gn b/ui/ozone/BUILD.gn
index ad01225..70a0b92b 100644
--- a/ui/ozone/BUILD.gn
+++ b/ui/ozone/BUILD.gn
@@ -62,7 +62,6 @@
   }
 }
 
-# GYP version: ui/ozone/ozone.gyp:ozone_base
 component("ozone_base") {
   sources = [
     "public/cursor_factory_ozone.cc",
@@ -173,7 +172,6 @@
   ]
 }
 
-# GYP version: ui/ozone/ozone.gyp:generate_ozone_platform_list
 action("generate_ozone_platform_list") {
   script = "generate_ozone_platform_list.py"
   outputs = [
@@ -193,7 +191,6 @@
   visibility += [ "//media:*" ]
 }
 
-# GYP version: ui/ozone/ozone.gyp:generate_constructor_list
 action("generate_constructor_list") {
   script = "generate_constructor_list.py"
 
diff --git a/ui/ozone/empty.cc b/ui/ozone/empty.cc
deleted file mode 100644
index 154ead76..0000000
--- a/ui/ozone/empty.cc
+++ /dev/null
@@ -1,6 +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.
-
-// This empty source file exists to force GYP to link the
-// ui/ozone/ozone.gyp:ozone target using the C++ compiler.
diff --git a/ui/ozone/platform/cast/BUILD.gn b/ui/ozone/platform/cast/BUILD.gn
index c7e1d04..377fcca 100644
--- a/ui/ozone/platform/cast/BUILD.gn
+++ b/ui/ozone/platform/cast/BUILD.gn
@@ -10,7 +10,6 @@
   "//chromecast/*",
 ]
 
-# GYP version: cast.gypi:ozone_platform_cast
 # TODO(slan): gn check needs deps on ozone and media to pass. Correct this.
 source_set("cast") {
   sources = [