RADV Driver Drops NGG Stream-Out Code For RDNA1/RDNA2 GPUs

While the original AMD Navi GPUs featured Next-Gen Geometry (NGG) support, it was borked for some GPUs and initially didn't work out quite as well as planned for vertex and geometry processing. The Mesa Radeon Vulkan driver "RADV" has worked on the NGG code for years and with RDNA3 GPUs it's finally been working out very well from the start and better than their legacy pipeline. All the while the RDNA1/RDNA2 experimental NGG stream-out support has continued to exist but hidden behind a feature/debug flag. That code is now being removed...