USB: serial: vizzini: remove outdated comment

I fixed up all of the #ifdef stuff, so remove the comment saying it
still needs to be removed.

Reported-by: Alan Cox <alan@lxorguk.ukuu.org.uk>
Cc: Rob Duncan <rob.duncan@exar.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>