Clean up PRESUBMIT.py - remove references to removed clang trybots

PRESUBMIT_test.py

 #!/usr/bin/env python
 # Copyright (c) 2012 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.
 
 import glob
 import json
 import os
 import re
 import subprocess
@@ skipping 703 matching lines @@
             'android_x86_dbg',
             'blink_android_compile_dbg',
             'blink_android_compile_rel',
             'blink_presubmit',
             'chromium_presubmit',
             'linux_arm_cross_compile',
             'linux_arm_tester',
             'linux_chromeos_asan',
             'linux_chromeos_browser_asan',
             'linux_chromeos_valgrind',
-            'linux_chromium_chromeos_clang_dbg',
-            'linux_chromium_chromeos_clang_rel',
             'linux_chromium_chromeos_dbg',
             'linux_chromium_chromeos_rel',
-            'linux_chromium_clang_dbg',
-            'linux_chromium_clang_rel',
             'linux_chromium_compile_dbg',
             'linux_chromium_compile_rel',
             'linux_chromium_dbg',
             'linux_chromium_gn_dbg',
             'linux_chromium_gn_rel',
             'linux_chromium_rel',
             'linux_chromium_trusty32_dbg',
             'linux_chromium_trusty32_rel',
             'linux_chromium_trusty_dbg',
             'linux_chromium_trusty_rel',
@@ skipping 32 matching lines @@
     }
     for master, bots in bots.iteritems():
       for bot in bots:
         self.assertEqual(master, PRESUBMIT.GetTryServerMasterForBot(bot),
                          'bot=%s: expected %s, computed %s' % (
             bot, master, PRESUBMIT.GetTryServerMasterForBot(bot)))
 
 
 if __name__ == '__main__':
   unittest.main()