Removes unused default_assignment_driver method
Removes unused default_assignment_driver method

Change-Id: I034352d8a8453b5e44e07de2087e6162df64cfe0

ilay09/keystone,openstack/keystone,rajalokan/keystone,mahak/keystone,openstack/keystone,ilay09/keystone,mahak/keystone,rajalokan/keystone,mahak/keystone,rajalokan/keystone,ilay09/keystone,openstack/keystone