Well, if I type in the URL and append #message=0 it works for me. But because with Forms you typically stream the PDF byte stream to the client instead of using URL's to actual PDF files that doesn't help much.
I tried to find a JavaScript way of doing it and asked around, but it doesn't appear that there is a way. I believe there has been an enhancement request made for that. So maybe in the future.
There is a menu option under Edit->Preferences->Forms to always hide it. If you open a PDF that makes it show, then check that, then opening PDF's after that will not show the message bar.
Chris
Adobe Enterprise Developer Support