MDL-54771 restore: Add deletesource to course object

Since deleting a course now triggers the pre_course_delete hook
it may be useful for hook implementations to know whether it was
a "true" course deletion, or one originating from a temporary
course created during a restore.

backup/util/ui/restore_ui.class.php

@@ -231,9 +231,11 @@ public function execute() {
      * Delete course which is created by restore process
      */
     public function cleanup() {
+        global $DB;
         $courseid = $this->controller->get_courseid();
-        if ($this->is_temporary_course_created($courseid)) {
-            delete_course($courseid, false);
+        if ($this->is_temporary_course_created($courseid) && $course = $DB->get_record('course', array('id' => $courseid))) {
+            $course->deletesource = 'restore';
+            delete_course($course, false);
         }
     }