The dependency field of the devices can be entered manually or it can update itself when a layer 2 map is created. If you remove the dependency manually, it will be populated again since by default the layer 2 map will have a auto-discovery interval.
To stop the auto update/population of dependency field - Connect to the DB - https://support.zoho.com/portal/manageengine/helpcenter/articles/connecting-to-the-opmanager-database
Execute - update layer2configuration set autodependency='false';
This will prevent the auto-updation of the dependency field.