Remove hack for ubuntu cloud archive

There is a hack here to set up ubuntu cloud archive, pinning it to
mirror.dfw.rax.openstack.org. The mirror-info role seems to be doing
this correctly now though, so let's remove the hack and let things work
normally.

Change-Id: I283cb3452245b64e9492806f06404b484f21c358

playbooks/pre.yaml

@@ -18,15 +18,3 @@
     - setup-devstack-cache
     - start-fresh-logging
     - write-devstack-local-conf
-  # TODO(jeblair): remove when configure-mirrors is fixed
-  tasks:
-    - name: Hack mirror_info
-      shell:
-        _raw_params: |
-          mkdir /etc/ci
-          cat << "EOF" > /etc/ci/mirror_info.sh
-          export NODEPOOL_UCA_MIRROR=http://mirror.dfw.rax.openstack.org/ubuntu-cloud-archive
-          EOF
-      args:
-        executable: /bin/bash
-      become: true