Remove text about OSC as a plugin requirement
Remove text about OSC as a plugin requirement

python-openstackclient should not be in a plugin's requirements.txt
as it will pull in the OSC dependencies that may not be desirable.

Change-Id: Id72745704ec70cab438e766dbac21a838fccb523

openstack/python-openstackclient,openstack/python-openstackclient,dtroyer/python-openstackclient,dtroyer/python-openstackclient