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/api/controller/binhost.py b/api/controller/binhost.py
index b5ae305..652eee6 100644
--- a/api/controller/binhost.py
+++ b/api/controller/binhost.py
@@ -6,8 +6,7 @@
 
 import os
 import shutil
-
-from six.moves import urllib
+import urllib.parse
 
 from chromite.api import controller
 from chromite.api import faux