Removed references to win_gpu, which has been removed

gpu/PRESUBMIT.py

Index: gpu/PRESUBMIT.py
diff --git a/gpu/PRESUBMIT.py b/gpu/PRESUBMIT.py
deleted file mode 100644
index 53fc15355050072dc52f6384327bded3d8032522..0000000000000000000000000000000000000000
--- a/gpu/PRESUBMIT.py
+++ /dev/null
@@ -1,16 +0,0 @@
-# Copyright (c) 2014 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.
-
-"""Top-level presubmit script for gpu/.
-
-See http://dev.chromium.org/developers/how-tos/depottools/presubmit-scripts
-for more details about the presubmit API built into depot_tools.
-"""
-
-def GetPreferredTryMasters(project, change):
-  return {
-    'tryserver.chromium.gpu': {
-      'win_gpu': set(['defaulttests']),
-    }
-  }