Re-enable F405 pep8 errors

Change-Id: I731686a144394b79e1e263cd73ee12a7a2d12914
diff --git a/tox.ini b/tox.ini
index 174a496..6a50c6d 100644
--- a/tox.ini
+++ b/tox.ini
@@ -51,6 +51,6 @@
 [flake8]
 # These are ignored intentionally in openstack-infra projects;
 # please don't submit patches that solely correct them or enable them.
-ignore = E305,E125,E129,E402,H,F405,W503
+ignore = E305,E125,E129,E402,H,W503
 show-source = True
 exclude = .venv,.tox,dist,doc,build,*.egg