Enable OAuth2 by default.

auth.py

Index: auth.py
diff --git a/auth.py b/auth.py
index 15fc15deb9033d08bf0370216902912fbe9ebad1..cc1b82b697f125abe02e7e1c4d1a288ea30e46ea 100644
--- a/auth.py
+++ b/auth.py
@@ -111,7 +111,7 @@ def make_auth_config(
   """
   default = lambda val, d: val if val is not None else d
   return AuthConfig(
-      default(use_oauth2, _should_use_oauth2()),
+      default(use_oauth2, True),
       default(save_cookies, True),
       default(use_local_webserver, not _is_headless()),
       default(webserver_port, 8090),
@@ -481,14 +481,6 @@ class Authenticator(object):
 ## Private functions.
 
 
-def _should_use_oauth2():
-  """Default value for use_oauth2 config option.
-
-  Used to selectively enable OAuth2 by default.
-  """
-  return os.path.exists(os.path.join(DEPOT_TOOLS_DIR, 'USE_OAUTH2'))
-
-
 def _is_headless():
   """True if machine doesn't seem to have a display."""
   return sys.platform == 'linux2' and not os.environ.get('DISPLAY')