mac: Delete more 10.5-only code

ui/gfx/scoped_ns_graphics_context_save_gstate_mac.mm

 // 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.
 
 #include "ui/gfx/scoped_ns_graphics_context_save_gstate_mac.h"
 
 #import <AppKit/AppKit.h>
 
 #include "base/logging.h"
-#include "base/mac/mac_util.h"
 
 namespace gfx {
 
 ScopedNSGraphicsContextSaveGState::ScopedNSGraphicsContextSaveGState()
     : context_([NSGraphicsContext currentContext]) {
   [NSGraphicsContext saveGraphicsState];
 }
 
 ScopedNSGraphicsContextSaveGState::~ScopedNSGraphicsContextSaveGState() {
   [NSGraphicsContext restoreGraphicsState];
-  if (!context_ && base::mac::IsOSLeopardOrEarlier()) {
-    // On 10.5 and earlier, there is a bug. If the current graphics context was
-    // nil when +[NSGraphicsContext saveGraphicsState] was called, then calling
-    // +[NSGraphicsContext restoreGraphicsState] will not restore a nil current
-    // context, but will leave the current context in place. Because allowing
-    // that stale context (which will be deallocated soon) to remain current
-    // will only lead to heartache and pain, the current context must be
-    // manually nilled out.
-    [NSGraphicsContext setCurrentContext:nil];
-  }
   DCHECK_EQ(context_, [NSGraphicsContext currentContext]);
 }
 
 }  // namespace gfx