Remove contiv related files (#6964)

.gitlab-ci/packet.yml

README.md

docs/_sidebar.md

docs/ci.md

docs/contiv.md

inventory/sample/group_vars/k8s-cluster/k8s-cluster.yml

inventory/sample/group_vars/k8s-cluster/k8s-net-contiv.yml

roles/download/defaults/main.yml

...kubernetes-apps/network_plugin/contiv/tasks/configure.yml

roles/kubernetes-apps/network_plugin/contiv/tasks/main.yml

roles/kubernetes-apps/network_plugin/meta/main.yml

roles/kubernetes/node/templates/kubelet.env.v1beta1.j2

roles/kubernetes/preinstall/tasks/0020-verify-settings.yml

...s/kubernetes/preinstall/tasks/0050-create_directories.yml

roles/kubespray-defaults/defaults/main.yaml

roles/network_plugin/contiv/defaults/main.yml

roles/network_plugin/contiv/files/contiv-cleanup.sh

roles/network_plugin/contiv/handlers/main.yml

roles/network_plugin/contiv/meta/main.yml

roles/network_plugin/contiv/tasks/main.yml