[llvm] [AMDGPU] Remove explicitly datalayout from tests where not needed (PR #137921)

[Shilei Tian via llvm-commits]

https://github.com/shiltian approved this pull request.

Thanks for the clean up. `target triple` should not be necessary as well but that would be in a separate PR.

https://github.com/llvm/llvm-project/pull/137921