validate - prune mongodb

roles/0-init/tasks/validate_vars.yml

@@ -85,7 +85,6 @@
       - kolibri
       - kiwix
       - moodle
-      - mongodb
       - sugarizer
       - osm_vector_maps
       - transmission

vars/default_vars.yml

@@ -471,10 +471,8 @@ moodle_enabled: False
 # This role was formerly installed by roles/sugarizer/meta/main.yml
 #
 # 2020-02-04: mongodb_install is completely ignored as MongoDB is installed on
-# demand as a dependency -- by Sugarizer -- but for now we set fake value
-# 'mongodb_install: True' so that 'mongodb_installed is defined' input
-# validation works, e.g. in 0-init/tasks/validate_vars.yml
-mongodb_install: True
+# demand as a dependency -- by Sugarizer
+mongodb_install: False
 # FYI 'mongodb_enabled: False' works when Sugarizer is disabled.  Required by
 # mongodb/tasks/enable.yml to shut down the service and log status, but that is
 # misleading as Sugarizer starts mongodb's systemd service on its own, due to