Remove subscriber check from newsletter validator

Checking the subscriber limit has nothing to do with the newsletter
itself, so it makes more sense to continue to perform that check as
needed elsewhere in the codebase.

MAILPOET-4236

mailpoet/lib/API/JSON/v1/Newsletters.php

@@ -25,6 +25,7 @@ use MailPoet\Newsletter\Scheduler\Scheduler;
 use MailPoet\Newsletter\Url as NewsletterUrl;
 use MailPoet\Settings\SettingsController;
 use MailPoet\UnexpectedValueException;
+use MailPoet\Util\License\Features\Subscribers as SubscribersFeature;
 use MailPoet\Util\Security;
 use MailPoet\WP\Emoji;
 use MailPoet\WP\Functions as WPFunctions;
@@ -63,6 +64,9 @@ class Newsletters extends APIEndpoint {
   /** @var Emoji */
   private $emoji;
 
+  /** @var SubscribersFeature */
+  private $subscribersFeature;
+
   /** @var SendPreviewController */
   private $sendPreviewController;
 
@@ -87,6 +91,7 @@ class Newsletters extends APIEndpoint {
     NewsletterListingRepository $newsletterListingRepository,
     NewslettersResponseBuilder $newslettersResponseBuilder,
     PostNotificationScheduler $postNotificationScheduler,
+    SubscribersFeature $subscribersFeature,
     Emoji $emoji,
     SendPreviewController $sendPreviewController,
     NewsletterSaveController $newsletterSaveController,
@@ -102,6 +107,7 @@ class Newsletters extends APIEndpoint {
     $this->newsletterListingRepository = $newsletterListingRepository;
     $this->newslettersResponseBuilder = $newslettersResponseBuilder;
     $this->postNotificationScheduler = $postNotificationScheduler;
+    $this->subscribersFeature = $subscribersFeature;
     $this->emoji = $emoji;
     $this->sendPreviewController = $sendPreviewController;
     $this->newsletterSaveController = $newsletterSaveController;
@@ -165,6 +171,12 @@ class Newsletters extends APIEndpoint {
       ]);
     }
 
+    if ($status === NewsletterEntity::STATUS_ACTIVE && $this->subscribersFeature->check()) {
+      return $this->errorResponse([
+        APIError::FORBIDDEN => __('Subscribers limit reached.', 'mailpoet'),
+      ], [], Response::STATUS_FORBIDDEN);
+    }
+
     $newsletter = $this->getNewsletter($data);
     if ($newsletter === null) {
       return $this->errorResponse([