Update stdpc5 and friends in iset.mm
Update stdpc5 and friends in iset.mm

- Copy-paste stdpc5 from set.mm. This makes it use F/.
- Add nfequid which is referred to in the stdpc5 comment.
- Revise sbalyz proof to use F/ more places.

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