remove deprecated bare variable (#167)

Author: FLiPp3r90

tasks/mongodb-RedHat.yml

@@ -34,7 +34,7 @@
     group: "root"
     mode: 0644
   when:
-    - use_system_d
+    - use_system_d | bool
   notify:
     - "reload systemd configuration"
     - "restart mongod"