MDL-70427 admin: remove plugin adhoc tasks during uninstall.

lib/adminlib.php

@@ -209,6 +209,7 @@ function uninstall_plugin($type, $name) {
     $DB->delete_records('event', ['component' => $component]);
 
     // Delete scheduled tasks.
+    $DB->delete_records('task_adhoc', ['component' => $component]);
     $DB->delete_records('task_scheduled', array('component' => $component));
 
     // Delete Inbound Message datakeys.

lib/tests/task_logging_test.php

@@ -441,6 +441,7 @@ class core_task_logmanager extends advanced_testcase {
      */
     protected function get_test_adhoc_task() : \core\task\adhoc_task {
         $task = $this->getMockForAbstractClass(\core\task\adhoc_task::class);
+        $task->set_component('core');
 
         // Mock a lock on the task.
         $lock = $this->getMockBuilder(\core\lock\lock::class)