Remove unnecessary submit handler for email_registration_form_user_admin_settings_alter

The current implementation of email_registration_form_user_admin_settings_alter uses an additional submit handler in order to set the module specific settings variables. However, as user_admin_settings calls system_settings_form, these variables will also be set by system_settings_form_submit. Hence, the additional submit handler is not needed and can be removed. Patch enclosed.