glx: Stop specifying GLX_DEPTH_SIZE
This code is just confused. It's asking for at least as many bits of (z-axis) depth as the root window has bits of (color) depth. For rgb565 or rgb888 this is harmless, but at 10 bits per channel this demands a 30-bit or deeper Z buffer. While some hardware could in principle do a 32-bit Z buffer, Mesa does not expose such fbconfigs (at least on Intel and AMD).
We're not actually using the Z buffer, so just stop asking for one.