Rewrite UserFlag entity to Doctrine

[MAILPOET-2014]

lib/Models/UserFlag.php

@@ -1,24 +0,0 @@
-<?php
-namespace MailPoet\Models;
-
-if (!defined('ABSPATH')) exit;
-
-/**
- * @property int $user_id
- * @property string $name
- * @property string $value
- */
-class UserFlag extends Model {
-  public static $_table = MP_USER_FLAGS_TABLE;
-
-  public static function createOrUpdate($data = []) {
-    $keys = false;
-    if (!empty($data['user_id']) && !empty($data['name'])) {
-      $keys = [
-        'user_id' => $data['user_id'],
-        'name' => $data['name'],
-      ];
-    }
-    return parent::_createOrUpdate($data, $keys);
-  }
-}