Revert "radv: keep track of whether NGG is used for GS on GFX10"

Revert "radv: keep track of whether NGG is used for GS on GFX10"

This reverts commit 63e0675d986744a9ed2d9a15b7cba84ff4a24fc2.

The GS is merged with the preceding shader and since the preceding
shader will have as_ngg set the final binary will have is_ngg set.

So we do not need the gs key here.

Reviewed-by: Samuel Pitoiset <samuel.pitoiset@gmail.com>