[MLIR][AMDGPU] Remove support for old llvm.amdgcn.buffer.* intrinsics (#93838)
They have been superseded by llvm.amdgcn.raw.buffer.* and llvm.amdgcn.struct.buffer.*.
They have been superseded by llvm.amdgcn.raw.buffer.* and llvm.amdgcn.struct.buffer.*.