Revert "Add additionalProperties to device schema (#6687)" (#6692)

This reverts commit eb930ac544.

lib/util/settings.schema.json

@@ -704,10 +704,6 @@
           "description": "Allows to prevent certain attributes from being published"
         }
       },
-      "additionalProperties": {
-        "type": "string",
-        "title": "Device specific property"
-      },
       "required": ["friendly_name"]
     },
     "group": {