Before this, the virtual VRAM was 32 bits per pixel, with each pixel
holding an 8-bit index color or 0x80RRGGBB. The latter was for Ayumi-
chan Monogatari Jisshaban, which has been unsupported since system3-sdl2
was forked from System3 for Win32.
This change removes the 0x80RRGGBB format and makes the virtual VRAM 8
bits per pixel.