add support for allowing deleting of individual user enrolments

    /**

     * Does this plugin allow manual unenrolments?

     *

     * @param stdClass $instance course enrol instance

     * All plugins allowing this must implement 'enrol/xxx:unenrol' capability

     *

     * @return bool - true means user with 'enrol/xxx:unenrol' may unenrol others freely, trues means nobody may touch user_enrolments

     */

    public function allow_unenrol(stdClass $instance) {

        return false;

    }

    /**

     * Does this plugin allow manual unenrolment of a specific user?

     * All plugins allowing this must implement 'enrol/xxx:unenrol' capability

     *

     * This is useful especially for synchronisation plugins that

     * do suspend instead of full unenrolment.

     *

     * @param stdClass $instance course enrol instance

     * @param stdClass $ue record from user_enrolments table

     *

     * @return bool - true means user with 'enrol/xxx:unenrol' may unenrol this user, false means nobody may touch this user enrolment

     */

    public function allow_unenrol_user(stdClass $instance, stdClass $ue) {

        return $this->allow_unenrol($instance);

    }