Minor fix for DEVFS=yes

If DEVFS=yes in bootcdwrite.conf and you're using devfs, the boot fails
saying it can't mount devfs.  This happens after the initial ram disk
has been processed.  There is no mount point on which to mount devfs.

Removing this line bootcdwrite fixes the problem:
[ "$DEVFS" = "yes" ] && run rm -r $VAR/input_dir/dev.ro