Adjust comment of f1dmex in iset.mm.
Adjust comment of f1dmex in iset.mm.

Most obviously, we don't have anything called ax-rep . More
subtly, there are forms of replacement which might be
equivalent (to each other or f1dmex) given excluded middle but
are not equivalent for us.

metamath/set.mm,metamath/set.mm,metamath/set.mm