gitlab: include task to prune unused docker images

After starting a new container with the latest version of GitLab, opt to remove older docker images so they do not take up disk space needlessly.

roles/gitlab/tasks/main.yml

@@ -102,8 +102,6 @@
 - name: prune unused docker images
   docker_prune:
     images: true
-    images_filters:
-      until: 960h
 
 - name: open firewall holes
   ansible.posix.firewalld: port={{ item }} permanent=true state=enabled immediate=yes