From my searching there doesnt seem to be a GPO to do this. I can remove the help link from the start menu, however there's still lots of ways to get into help through explorer windows or by pressing F1 for example.
I was thinking a software policy to disallow C:\Windows\winhlp32.exe from running would do the job. I've done this and I can still access help.
Win 7, Server 2008 R2