Remove gpu bots from sub-directory PRESUBMITs.

ui/gl/PRESUBMIT.py

-# 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 ui/gl/.
-
-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': {
-      'linux_gpu': set(['defaulttests']),
-      'mac_gpu': set(['defaulttests']),
-      'win_gpu': set(['defaulttests']),
-    }
-  }