ui: remove 'ws_tls' field from VncState

The 'ws_tls' field in VncState is only ever representing
the result of 'tlscreds != NULL' and is thus pointless.
Replace use of 'ws_tls' with a direct check against
'tlscreds'

Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
Message-id: 1475163940-26094-4-git-send-email-berrange@redhat.com
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
