Drop django_openstack_auth from requirements.txt
Drop django_openstack_auth from requirements.txt

django_openstack_auth has been merged into horizon tree
as an effort of blueprint merge-openstack-auth.
There is no need to depend on django_openstack_auth any more.

Change-Id: Idc7ce5451ce5eb42ff53fc7d84066a7b10fd9f16

openstack/designate-dashboard,openstack/designate-dashboard,openstack/designate-dashboard