Remove build references to third_party/cygwin

There's test running dependencies in blink and buildbot,
so the directory/DEPS can't be removed right now. For the
time being, remove the build related entries.

R=maruel@chromium.org, thakis@chromium.org
BUG=123026
TEST=remove from DEPS and .DEPS.git, delete HKCU\Software\Cygnus Solutions\... and build successfully.

Review URL: https://codereview.chromium.org/149063008

git-svn-id: http://src.chromium.org/svn/trunk/src/build@248802 4ff67af0-8c30-449e-8e8b-ad334ec8d88c

common.gypi

@@ -4557,7 +4557,6 @@
           '<(windows_sdk_path)/Include/winrt',
           '$(VSInstallDir)/VC/atlmfc/include',
         ],
-        'msvs_cygwin_dirs': ['<(DEPTH)/third_party/cygwin'],
         'msvs_cygwin_shell': 0,
         'msvs_disabled_warnings': [4351, 4355, 4396, 4503, 4819,
           # TODO(maruel): These warnings are level 4. They will be slowly

win/setup_cygwin_mount.py

@@ -1,20 +0,0 @@
-# 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 os
-import sys
-
-def main():
-  if len(sys.argv) != 2 or sys.argv[1] != '--win-only':
-    return 1
-  if sys.platform in ('win32', 'cygwin'):
-    self_dir = os.path.dirname(sys.argv[0])
-    mount_path = os.path.join(self_dir, "../../third_party/cygwin")
-    batch_path = os.path.join(mount_path, "setup_mount.bat")
-    return os.system(os.path.normpath(batch_path) + ">nul")
-  return 0
-
-
-if __name__ == "__main__":
-  sys.exit(main())