radeonsi: remove special handling of TGSI_INTERPOLATE_COLOR in shader codegen

It doesn't do anything useful. And colors are floating-point, so we can use
fs.interp, remove "flatshade" from the shader key, and rely on the FLAT_SHADE
state only (in the next patch).

Reviewed-by: Michel Dänzer <michel.daenzer@amd.com>
1 file changed