Remove heap.h

[Mike Hearn]

On Thu, 30 Dec 2004 15:41:06 -0500, Dimitrie O. Paun wrote:
> To be honest, I'm not too happy with this patch, HEAP_strdupWtoA
> was a good marker for code that needed fixing, this patch just
> makes those places harder to find.

I don't really understand why we can't make this an inline or something,
it seems that it's a lot more convenient than the direct win32
equivalents. Making it an inline would achieve the same effect as simply
replacing each usage manually, and allow us to improve DLL separation as
well.