glsl: drop NMS OpenGL workarounds

No Mans Sky dropped its OpenGL backend on April 16, 2019 in favour
of its Vulkan backend. So here we drop the old OpenGL workarounds.

Reviewed-by: Marek Olšák <marek.olsak@amd.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/7362>
10 files changed