Implement new delete_instance callback.

[sumaiyamannan]

Hi,

Currently a capquiz activity cannot be deleted. It gets deleted and then goes to the recycle bin. See details here in the report issue #206

Testing instructions

• Create a new capquiz activity with questions and publish it
• Delete the activity and run cron. You will see the below error stack

Adhoc task failed: core_course\task\course_delete_modules,Coding error detected, it must be fixed by a programmer: The course module 6 could not be deleted. Can't find data record in database. (SELECT cm.*, m.name, md.name AS modname 
              FROM {course_modules} cm
                   JOIN {modules} md ON md.id = cm.module
                   JOIN {capquiz} m ON m.id = cm.instance
                   
             WHERE cm.id = :cmid AND md.name = :modulename
                   
[array (
  'cmid' => 3,
  'modulename' => 'capquiz',
)]): /var/www/html/lib/dml/moodle_database.php(1682) #0 /var/www/html/lib/datalib.php(1266): moodle_database->get_record_sql('SELECT cm.*, m....', Array, 2)
#1 /var/www/html/mod/capquiz/classes/capquiz.php(75): get_coursemodule_from_id('capquiz', 1, 0, false, 2)
#2 /var/www/html/mod/capquiz/lib.php(67): mod_capquiz\capquiz->__construct(1)
#3 /var/www/html/course/lib.php(907): capquiz_delete_instance(1)
#4 /var/www/html/course/classes/task/course_delete_modules.php(66): course_delete_module('6')
#5 /var/www/html/lib/cronlib.php(367): core_course\task\course_delete_modules->execute()
#6 /var/www/html/lib/cronlib.php(198): cron_run_inner_adhoc_task(Object(core_course\task\course_delete_modules))
#7 /var/www/html/lib/cronlib.php(76): cron_run_adhoc_tasks(1706240953)
#8 /var/www/html/admin/cli/cron.php(178): cron_run()

Regards,
Sumaiya