AMDGPU: Remove r600 local id annotations in AMDGPULowerIntrinsics

With these dropped and memory intrinsic moved into a generic pass, we
can drop the whole pass.

No tests fail with this removed. The new amdgcn intrinsics are
annotated in clang up front.  Theoretically may regress r600, but that
would need new testing and support work (r600 ideally would also
follow the clang handling). The regression would be any IR passes
making use of known bits between this point and codegen. The DAG
computeKnownBits understand the intrinsics directly now.

If we wanted to refine these values, a better place would be in
AMDGPUAttributor.