Remove bogus path in tox.ini's flake8 exclude
Remove bogus path in tox.ini's flake8 exclude

It referenced os_collect_config's oslo-incubator path, and
os-refresh-config has neither.

Change-Id: I5d79c3595b1abc564c0e8f39d09bdff5361b45e5

openstack/os-refresh-config,openstack/os-refresh-config