docker-gc: remove unused var

roles/openshift_docker_gc/defaults/main.yml

@@ -1,5 +1,4 @@
 ---
-r_enable_docker_gc: "{{ openshift_crio_enable_docker_gc }}"
 r_docker_gc_node_selectors: "{{ openshift_crio_docker_gc_node_selector | default({'runtime': 'cri-o'}) }}"
 
 openshift_docker_gc_image_dict: