cs: fix $value confusion in schemify and begin0

The attempted repair for `$value` in 6c195d521c was wrong.

racket/src/cs/rumble/begin0.ss

@@ -3,8 +3,6 @@
 (define-syntax begin0
   (syntax-rules (void)
     [(_ expr0) expr0]
-    [(_ expr0 (void)) ; detect this pattern as a way of accessing the `$value` form
-     ($value expr0)]
     [(_ expr0 expr ...)
      (call-with-values (lambda ()
                          (call-with-values (lambda () expr0)

racket/src/schemify/interpret.rkt

@@ -613,7 +613,8 @@
                       (apply values new-stack vals))
                   (loop (fx+ i 1) new-stack)))))]
         [#($value ,e)
-         (begin0 (interpret e stack) (void))]
+         (let ([v (interpret e stack)])
+           v)]
         [#(clear ,clears ,e)
          (let loop ([clears clears] [stack stack])
            (cond