Remove some debug output

os.rkt

@@ -1,7 +1,5 @@
 #lang racket/base
 
-(require racket/pretty)
-
 ;; Virtualized operating system.
 
 (require racket/match)
@@ -160,7 +158,6 @@
 ;; VM -> KernelModeTransition
 ;; (A kind of Meta-InterruptK)
 (define (run-vm state)
-  (pretty-print `(run-vm ,state))
   (let* ((state (requeue-pollers state))
 	 (state (run-runnables state))
 	 (state (dispatch-messages state)))
@@ -342,6 +339,8 @@
 
 ;---------------------------------------------------------------------------
 
+(require racket/pretty)
+
 (define (yield k)
   (kernel-mode-transition (subscription 'none (lambda (_) (k)) '() '())
 			  '()