a plugin of mine stores user-specific settings in the usermeta table. If the plugin is uninstalled, I would like to delete this setting for all users. How is the right way to remove the settings for all users in the database? I found the function delete_usermeta, but this requires a UserID, so I would have to first determine all users and then go into a loop over it.
What should I consider in the context of a MU installation?