glx: Downgrade sRGB-ful fbconfigs
Again, NVIDIA supports this on every fbconfig, Mesa alternates it on and off for some reason but only on some drivers, and in particular llvmpipe doesn't try to create sRGB-ful fbconfigs. Nerf it out of the fbconfig. Acked-By:Mike Blumenkrantz <michael.blumenkrantz@gmail.com> Part-of: <mesa/mesa!1648>