Replace unsubscribe link short code strings by constant

[MAILPOET-2245]

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

@@ -42,7 +42,7 @@ class Links {
     $settings = new SettingsController();
     if ((boolean)$settings->get('tracking.enabled')) {
       $link_hash = NewsletterLinkModel::where('queue_id', $queue->id)
-        ->where('url', '[link:subscription_unsubscribe_url]')
+        ->where('url', NewsletterLinkModel::UNSUBSCRIBE_LINK_SHORT_CODE)
         ->findOne();
       if (!$link_hash instanceof NewsletterLinkModel) {
         return '';

lib/Cron/Workers/StatsNotifications/Worker.php

@@ -157,7 +157,7 @@ class Worker {
 
   public static function getShortcodeLinksMapping() {
     return [
-      '[link:subscription_unsubscribe_url]' => __('Unsubscribe link', 'mailpoet'),
+      NewsletterLink::UNSUBSCRIBE_LINK_SHORT_CODE => __('Unsubscribe link', 'mailpoet'),
       '[link:subscription_manage_url]' => __('Manage subscription link', 'mailpoet'),
       '[link:newsletter_view_in_browser_url]' => __('View in browser link', 'mailpoet'),
     ];

lib/Newsletter/Shortcodes/ShortcodesHelper.php

@@ -3,6 +3,7 @@
 namespace MailPoet\Newsletter\Shortcodes;
 
 use MailPoet\Models\CustomField;
+use MailPoet\Models\NewsletterLink;
 use MailPoet\WP\Functions as WPFunctions;
 
 class ShortcodesHelper {
@@ -82,7 +83,7 @@ class ShortcodesHelper {
           'text' => WPFunctions::get()->__('Unsubscribe link', 'mailpoet'),
           'shortcode' => sprintf(
             '<a target="_blank" href="%s">%s</a>',
-            '[link:subscription_unsubscribe_url]',
+            NewsletterLink::UNSUBSCRIBE_LINK_SHORT_CODE,
             WPFunctions::get()->__('Unsubscribe', 'mailpoet')
           ),
         ],