stubdom: fix compilation

diff -r 7d8892a90c90 extras/mini-os/lib/sys.c
@@ -188,7 +188,6 @@ int open(const char *pathname, int flags
         }
         default:
             printk(" unsupported flags\n");
-            stack_walk();
             do_exit();
     }
     if (fs_fd < 0) {