freshmaker/backend: Replace the yum module by the package module

Drop the use of with_items, it is deprecated in these modules and
it was not used in this role anyway...

Signed-off-by: Pierre-Yves Chibon <pingou@pingoured.fr>

roles/freshmaker/backend/tasks/main.yml

@@ -1,12 +1,9 @@
 ---
 - name: install the latest Freshmaker package
-  yum:
+  package:
     name: freshmaker
     state: latest
     update_cache: yes
-  with_items:
-  - freshmaker
-  - python2-odcs-client
   when: freshmaker_upgrade
   notify:
   - restart fedmsg-hub