radeonsi: don't try to eliminate trivial VS outputs for PS and CS
radeonsi: don't try to eliminate trivial VS outputs for PS and CS

PS and CS don't have any param exports, so it's a no-op.

Reviewed-by: Nicolai Hähnle <0d0be6cf5ad662651be2dc5dfd44aa2b09d4c1cc@amd.com>

metora/MesaGLSLCompiler,metora/MesaGLSLCompiler,metora/MesaGLSLCompiler