ui/console: remove new_console()

The constructor helper isn't of much used now.

"head" is only specified for graphic console (and default to 0), and we
are going to move it to QemuGraphicConsole next.

Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
Message-Id: <20230830093843.3531473-23-marcandre.lureau@redhat.com>