ui/console: replace QEMUFIFO with Fifo8

One of the two FIFO implementations QEMUFIFO and Fifo8 is
redundant. Replace QEMUFIFO with Fifo8.

Signed-off-by: Volker Rümelin <vr_qemu@t-online.de>
Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Message-Id: <20210916192239.18742-1-vr_qemu@t-online.de>
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>