title: remove many to many association symfony 3.4
body: <p>I have two entity "Product" and "User" with ManyToMany association.
  and I want to add columns to this association .
   to do that i must create another entity and linked between them with a one-to-many and many-to-one relation.
  so the problem is how to delete the first association "ManyToMany"</p>
  
  <p>from:</p>
  
  <pre><code>class Product
  {
      /**
       * @ORM\ManyToMany(targetEntity="User", mappedBy="products")
       */
      private $users;
  }
  </code></pre>
  
  <pre><code>class User extends BaseUser
  {
      /**
       * @ORM\ManyToMany(targetEntity="ManagementBundle\Entity\Product", inversedBy="users")
       * @ORM\JoinTable(name="users_products")
       */
      protected $products;
  }
  </code></pre>
  
  <p>to:</p>
  
  <pre><code>class Product
  {
      /**
       * @ORM\ManyToOne(targetEntity="OrderProduct", inversedBy="products",cascade={"persist"})
       * @ORM\JoinColumn(name="OrderProduct_id", referencedColumnName="id")
       */
      private $OrderProduct;
  }
  </code></pre>
  
  <pre><code>class User extends BaseUser
  {
      /**
       * @var string
       *
       * @ORM\OneToMany(targetEntity="OrderProduct", mappedBy="user",cascade={"persist"})
       */
      protected $orderProducts;
  }
  </code></pre>
  
  <pre><code>class OrderProduct
  {
  
      /**
       * @ORM\ManyToOne(targetEntity="User", inversedBy="OrderProducts",cascade={"persist"})
       * @ORM\JoinColumn(name="user_id", referencedColumnName="id")
       */
      private $user;
  
      /**
       * @var string
       *
       * @ORM\OneToMany(targetEntity="Product", mappedBy="OrderProduct",cascade={"persist"})
       */
      private $products;
  }
  </code></pre>