Revert "fix double-expansion in `class`"
Revert "fix double-expansion in `class`"

This reverts commit 005b3f720f94bb2cc78b6586de79b045f568494b.

The expander's definition of "same context" is not flexible
enough, and introducing an extra `#%expression` wrapper
breaks TR's recognition of expanded classes. Revisit in the
near future.

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