Remove leftovers of "# noqa"

This patch set removes leftovers of "# noqa" from imports
added to import_exceptions.

It also adds "django.test.utils.override_settings" to
import_exceptions, so a few more "# noqa" tags become
unnecessary.

Closes-Bug: #1273647

Change-Id: I39f856ac3ea371a2fcab272bbf358d0243164b6d
Merge "Remove leftovers of "# noqa""