systemd: remove ceph-create-keys from presets

systemd: remove ceph-create-keys from presets

ceph-create-keys unit file was removed here:

* https://github.com/ceph/ceph/commit/8bcb4646b6b9846bb965cdec3ca2a21eb3b26bab
* https://github.com/ceph/ceph/commit/dc5fe8d415858358bd0baf5d8dce0a753f5e0cea

As a consequence the systemctl preset command now fails to run since the
unit does not exist anymore. Due to the redirection in /dev/null we
don't know what's happening.

Ultimately the mon unit doesn't get enabled and the mon service won't
start after reboot.
Removing the old/non-existent unit makes the command succeed now.

Signed-off-by: Sébastien Han <seb@redhat.com>
(cherry picked from commit 151c0ce213186b2196531ce74478ed7671eb9819)