nir/lower_gs_intrinsics: Remove end primitive for points
EndPrimitive() for points is entirely pointless, so just remove it when lowering EndPrimitive to simplify the IR. This is (maybe) an optimization everywhere, and will be relied on for correctness on Asahi.
I don't really need this merged, it would be straightforward to ignore EndPrimitive for points in the backend (rather than asserting that it doesn't happen). But this seems like an obviously good idea to do in the core if we're lowering EndPrimitive anyway
Edited by Alyssa Rosenzweig