fix double-expansion in `class`
fix double-expansion in `class`

The `class` macro uses `synatx-local-expand-expression`, but it
discarded the result and used the original, which implies
re-expanding.

mafagafogigante/racket,mafagafogigante/racket,mafagafogigante/racket,mafagafogigante/racket,mafagafogigante/racket,mafagafogigante/racket,mafagafogigante/racket,mafagafogigante/racket,mafagafogigante/racket