ui/console: Remove qemu_create_display_surface_guestmem()

The qemu_create_display_surface_guestmem() function was added in
commit a77549b3 but apparently never used. Remove it.

(The API of this function is in any case awkward as a generic
function: it assumes that a physical address uniquely identifies
a piece of memory in the system, which is mostly but not
always true.)

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Message-id: 20181122170309.4856-1-peter.maydell@linaro.org
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>