Don't force msvs 2010 version when running gyp

tools/gyp_dart.py

 #!/usr/bin/env python
 
 # Copyright (c) 2012 The Dart Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 """
 Invoke gyp to generate build files for building the Dart VM.
 """
 
@@ skipping 15 matching lines @@
     component = sys.argv[1]
 
   component_gyp_files = {
     'all' : 'dart.gyp',
     'runtime' : 'runtime/dart-runtime.gyp',
   }
   args = ['python', '-S', 'third_party/gyp/gyp_main.py',
           '--depth=.', '-Itools/gyp/all.gypi',
           component_gyp_files[component]]
 
-  if sys.platform == 'win32':
-    # Generate Visual Studio 2010 compatible files by default.
-    if not os.environ.get('GYP_MSVS_VERSION'):
-      args.extend(['-G', 'msvs_version=2010'])
-
   sys.exit(execute(args))
 
 if __name__ == '__main__':
   main()