radv: Remove NV_mesh_shader.
NV_mesh_shader was a good tool for initial bringup of mesh shaders in RADV, but it was always meant to me superseded by the cross-vendor Vulkan extension EXT_mesh_shader. We never officially supported NV_mesh_shader and users had been warned not to use it. The only reason we kept it for this long is because it took a long time to get EXT_mesh_shader tested in CI.
Reasons for why we don't want to maintain the current level of support anymore:
- Difficult to efficiently support on RDNA3 (new fast launch doesn't support first task)
- It was already not fully supported on RDNA2, eg. indirect dispatch was a hack
- What worked, was inefficient
Based on !22128 (merged) to avoid conflicts.