rolling-update: remove old condition

This failure condition was only valid at the time where clusters didn't
have ceph-mgr activated. Now since we collocate the ceph-mgr with the
mon by default, if the daemon wasn't present it will be created during
the upgrade.

Signed-off-by: Sébastien Han <seb@redhat.com>

infrastructure-playbooks/rolling_update.yml

@@ -36,12 +36,6 @@
            invoking the playbook"
       when: ireallymeanit != 'yes'
 
-    - name: fail if no mgr host is present in the inventory
-      fail:
-        msg: "Please add a mgr host to your inventory."
-      when:
-        - groups.get(mgr_group_name, []) | length == 0
-
 
 - name: gather facts and check the init system