In Sitecore 9, the ProxyDisabler have been retired completely

Sitecore have finally retired the ProxyDisabler in Sitecore 9. Proxy items were the early version of item cloning and were deprecated in Sitecore 6. And now the ProxyDisabler have been removed.

There are no replacement. All you need to do is to remove the line from your code.

// Old Sitecore 5,6,7,8 code:
public void Put(Item source)
{
  using (new ProxyDisabler())
  {
    // Do stuff with your item
  }
}

// New Sitecore 9 code:
public void Put(Item source)
{
  // Do stuff with your item
}

MORE TO READ:

• Clone and Unclone an Item by Sitecore
• Using Proxy Items in Sitecore 5.3 by Sitecore