Leandro Ribeiro authored Dec 04, 2019 and Daniel Stone committed Dec 11, 2019

Remove member preferred_format from struct window and hardcode
ARGB32 pixel format for clients/window.

The member preferred_format was first added to allow hinting
of a preference for RGB565 when creating a window. But it is
not being used for a long time now. So it's safe to remove it
from the code, dropping support for RGB565 in clients/window.

Signed-off-by: Leandro Ribeiro <leandrohr@riseup.net>