fix wrong namespace use

apps/backend/app/Notifications/UserRegistered.php

@@ -6,9 +6,7 @@ use app\Models\User;
 use Illuminate\Bus\Queueable;
 use Illuminate\Contracts\Broadcasting\ShouldBroadcast;
 use Illuminate\Notifications\Messages\BroadcastMessage;
-use Illuminate\Notifications\Messages\MailMessage;
 use Illuminate\Notifications\Notification;
-use Illuminate\Support\Facades\Mail;
 
 class UserRegistered extends Notification implements ShouldBroadcast
 {