Yes, localhost and localhost.localdomain are still there in the headers.
Here is what I have been experimenting with in postfix_header_checks.in:
/^Received:.*from localhost (localhost.localdomain [127.0.0.1])/ IGNORE
Evidently not having .* is important as it throws errors if you don't have it.
This link was where I got some ideas from:
However he has spaces after his Received: lines then .*
I think it should be
You can see that he gets errors at the top of his post. I do as well if I have the word "from" more than twice.