Revert of [build] Use MSVS 2015 by default.

tools/mb/mb.py

 #!/usr/bin/env python
 # Copyright 2016 the V8 project authors. All rights reserved.
 # Copyright 2015 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.
 
 """MB - the Meta-Build wrapper around GYP and GN
 
 MB is a wrapper script for GYP and GN that can be used to generate build files
 for sets of canned configurations and analyze them.
@@ skipping 759 matching lines @@
           gn_labels.append(gn_isolate_map[target_name]['label'])
 
       if err:
           raise MBErr('Error: Failed to match swarming targets to %s:\n%s' %
                       ('//testing/buildbot/gn_isolate_map.pyl', err))
 
       gn_runtime_deps_path = self.ToAbsPath(build_dir, 'runtime_deps')
       self.WriteFile(gn_runtime_deps_path, '\n'.join(gn_labels) + '\n')
       cmd.append('--runtime-deps-list-file=%s' % gn_runtime_deps_path)
 
-    # Override msvs infra environment variables.
-    # TODO(machenbach): Remove after GYP_MSVS_VERSION is removed on infra side.
-    env = {}
-    env.update(os.environ)
-    env['GYP_MSVS_VERSION'] = '2015'
-
-    ret, _, _ = self.Run(cmd, env=env)
+    ret, _, _ = self.Run(cmd)
     if ret:
         # If `gn gen` failed, we should exit early rather than trying to
         # generate isolates. Run() will have already logged any error output.
         self.Print('GN gen failed: %d' % ret)
         return ret
 
     android = 'target_os="android"' in vals['gn_args']
     for target in swarming_targets:
       if android:
         # Android targets may be either android_apk or executable. The former
@@ skipping 700 matching lines @@
   # Then check to see if the arg contains any metacharacters other than
   # double quotes; if it does, quote everything (including the double
   # quotes) for safety.
   if any(a in UNSAFE_FOR_CMD for a in arg):
     arg = ''.join('^' + a if a in ALL_META_CHARS else a for a in arg)
   return arg
 
 
 if __name__ == '__main__':
   sys.exit(main(sys.argv[1:]))