gallivm: rip out unused lp_build_tgsi_aos

This isn't in use in-tree, and it doesn't really seem like it has received any real support for the last 7 years, apart from the obvious "let's keep it compiling"-commits.

So I suspect that nobody, even VMware cares about this at this point. So let's remove it, as it seems to contain some minor mistakes that can lead people astray when trying to figure out the details here.