radeonsi: fix VS kill_outputs handling
981bd8cb moved outputs removing handling to NIR, but instead of applying it only to the last stage before the FS this now applies it to both the GS and the VS.
This commit fixes this by clearing the kill_outputs field for the VS when using a ES-GS shader.
Fixes: 981bd8cb ("radeonsi: apply key.ge.opt.kill_{outputs,pointsize,clipdistance} in NIR")