glthread: fix a perf regression due to draw_always_async flag, fix DrawIndirect
Performance regressed by 31% in one VP2020/Creo subtest because the draw_always_async flag wasn't implemented correctly. Remove it instead of fixing it.
While removing it, I noticed that our DrawIndirect async conditions were incorrect. I fixed them.
Fixes: 3b897719 - glthread: add ctx->GLThread.draw_always_async to simplify draw checking