This reverts commit 9e1632ad.

Older gtk-vnc versions can't deal with non-incremental update
requests sending pseudo-encodings, so trying to send full server
state (including desktop size, cursor etc. which is done using
pseudo-encodings) doesn't fly.  Return to old behavior to send
those only for new connects and when changes happen.

Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
Tested-by: Laszlo Ersek <lersek@redhat.com>
Message-Id: <20210125104041.495274-2-kraxel@redhat.com>