Remove Python 3 warning.

Running on Python 3 should be a fairly common situation at this
point, so it doesn't seem like we need an explicit warning for it.

Change-Id: Id73ffb89f6da6e7268fd2e5963cf99175a47b5b7
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/2284547Reviewed-by: Edward Lesmes <ehmaldonado@chromium.org>
Commit-Queue: Dirk Pranke <dpranke@google.com>

gclient.py

@@ -118,18 +118,6 @@ import setup_color
 
 from third_party import six
 
-# Warn when executing this script with Python 3 when the GCLIENT_PY3 environment
-# variable is not set to 1.
-# It is an increasingly common error on Windows 10 due to the store version of
-# Python.
-if (sys.version_info.major >= 3
-    and not 'GCLIENT_TEST' in os.environ
-    and os.getenv('GCLIENT_PY3') != '1'):
-  print('Warning: Running gclient on Python 3. \n'
-        'If you encounter any issues, please file a bug on crbug.com under '
-        'the Infra>SDK component.', file=sys.stderr)
-
-
 # TODO(crbug.com/953884): Remove this when python3 migration is done.
 if six.PY3:
   # pylint: disable=redefined-builtin