Remove useless iso8601 requirements
Remove useless iso8601 requirements

This patch cleans up the requirements.txt list to remove
iso8601 module not used anymore.

Change-Id: I9d828297dee0a9a01bde8f8b84c505fd8b5603d1

openstack/sahara-dashboard,openstack/sahara-dashboard,openstack/sahara-dashboard,openstack/sahara-dashboard