The '--enable-vnc-tls' option to configure was removed in

  commit 3e305e4a
  Author: Daniel P. Berrange <berrange@redhat.com>
  Date:   Thu Aug 6 14:39:32 2015 +0100

    ui: convert VNC server to use QCryptoTLSSession

This removes the corresponding help string.

Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>