Remove non-existent ceph-internal repo

Ceph packages are installed from cta-ci-ceph-nautilus repository located in continuousintegration/docker/ctafrontend/cc7/etc/yum.repos.d/cta-ci.repo

continuousintegration/buildtree_runner/vmBootstrap/ceph-internal.repo

-[ceph-internal]
-name=ceph-internal
-enabled=1
-baseurl=http://castorwww.web.cern.ch/castorwww/repos/ceph/
-priority=4