Remove use_skia_on_mac.gypi ; building with CG is no longer supported.

build/use_skia_on_mac.gypi

Index: build/use_skia_on_mac.gypi
===================================================================
--- build/use_skia_on_mac.gypi	(revision 126639)
+++ build/use_skia_on_mac.gypi	(working copy)
@@ -1,9 +0,0 @@
-# Copyright (c) 2011 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.
-
-# Whether the Mac port uses Skia (instead of Core Graphics) by default.
-# This overrides the setting in common.gypi .
-{
-  'use_skia_on_mac%': 1,
-}