Remove iso8601 from dependencies
Remove iso8601 from dependencies

Our usage of this is now handled within oslo.utils.timeutils

Change-Id: I7eb26590afb8e42e5884f0e15d2387a11d58d76c

stackforge/python-openstacksdk,stackforge/python-openstacksdk,briancurtin/python-openstacksdk,briancurtin/python-openstacksdk,dtroyer/python-openstacksdk,dudymas/python-openstacksdk,mtougeron/python-openstacksdk,dtroyer/python-openstacksdk,mtougeron/python-openstacksdk,openstack/python-openstacksdk,dudymas/python-openstacksdk,openstack/python-openstacksdk