Remove validate-all-maintainers.sh
Remove validate-all-maintainers.sh

This checks Dockerfiles, which we don't currently have.

Change-Id: Ia07ba0a51ab8bdc13fb9075a401fe32d7612aaa4

asalkeld/kolla-mesos,openstack/kolla-mesos,openstack/kolla-mesos,openstack/kolla-mesos