There is a method you can use to delete attributes that are no longer needed from the database.
This method deletes all the attribute values of the bundle from the database. If the bundle is used by the administrator (see parameter ADMIN in the constructor method of the bundle concerned) the general values, which are valid for all users, are deleted. In the other case the user-specific values are then deleted.
For more information, see the documentation on IF_CUSTOMIZING~DELETE in the class builder.
There is another method you can use to delete the graphic proxy's reference to the customizing bundle instead of deleting attributes on the database. For more information, see Assigning Customizing Bundles to Proxies.