912442-candlepin-cert - do not overwrite candlepin-upstream-ca.crt

With candlepin 0.7.25, manifests signature checking is turned on by default. 'katello-configure' was incorrectly overwriting candlepin-upstream-ca.crt put down by the candlepin RPM with a symlink.

https://bugzilla.redhat.com/show_bug.cgi?id=912442