- Renames TaskScheduler to CronTrigger and updates relevant code

- Standardizes setting value const naming convention

lib/Cron/Workers/SendingQueue/Tasks/Cron.php

@@ -0,0 +1,18 @@
+<?php
+namespace MailPoet\Cron\Workers\SendingQueue\Tasks;
+
+use MailPoet\Cron\CronHelper;
+use MailPoet\Cron\CronTrigger;
+
+if(!defined('ABSPATH')) exit;
+
+class Cron {
+  static function complete() {
+    // when there are no more queues to process and if the task
+    // scheduler method is WP, delete the cron daemon
+    $task_scheduler = CronTrigger::getCurrentMethod();
+    if($task_scheduler === CronTrigger::METHOD_WORDPRESS) {
+      CronHelper::deleteDaemon();
+    }
+  }
+}