clean up usage of the six module

Now that we only support Python 3, we can drop all six usage.

BUG=b:187789302
TEST=CQ passes

Change-Id: I92ec7022f1f92fccc7d82ef3f262557081c0fc1b
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/chromite/+/2910860
Tested-by: Mike Frysinger <vapier@chromium.org>
Auto-Submit: Mike Frysinger <vapier@chromium.org>
Commit-Queue: Chris McDonald <cjmcdonald@chromium.org>
Reviewed-by: Chris McDonald <cjmcdonald@chromium.org>
diff --git a/scripts/cros_sdk.py b/scripts/cros_sdk.py
index 3d3fe72..9b22a1c 100644
--- a/scripts/cros_sdk.py
+++ b/scripts/cros_sdk.py
@@ -20,8 +20,7 @@
 import resource
 import subprocess
 import sys
-
-from six.moves import urllib
+import urllib.parse
 
 from chromite.lib import constants
 from chromite.lib import commandline