radeonsi: kill point size VS output if it's not used by the rasterizer

Fixed-func shaders can contain the output, because their generator
doesn't consider the current primitive type into account.

Acked-by: Pierre-Eric Pelloux-Prayer <pierre-eric.pelloux-prayer@amd.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/6620>
5 files changed