Remove distinct variable constraints in iset.mm
Remove distinct variable constraints in iset.mm

This is between G and x in frec2uzzd and frec2uzsucd . It seems
better to put the variable changes (where needed) within
these theorems, rather than making proofs which use them do it.

set.mm lacks a distinct variable constraint between G and x
in om2uzsuci so in that sense this puts things back the way
they had been.

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