Get rid of unnecessary form_id in form alters to reduce errors from undefined variable

I'm building custom forms based on register form, that's why need to fire up alters manually. In current version I have to do something like this:
email_registration_form_user_register_form_alter($form, $form_state['object'], 'user_register_form');
though it's better to get rid of 3d variabe $form_id which is useless of hook_form_FORM_ID_alter:
email_registration_form_user_register_form_alter($form, $form_state['object']);