[llvm] [SeparateConstOffsetFromGEP] Remove support for arithmetic lowering (PR #151477)

[Karthika Devi C via llvm-commits]

kartcq wrote:

Hi @nikic @arsenm 
In this PR, I am observing **llvm/test/CodeGen/AArch64/aarch64-gep-opt.ll** has not been entirely updated.
There are unused checks in the file.
Please let me know if the observation is correct.
If so, I can push a patch to clean up that file.
Thanks.

https://github.com/llvm/llvm-project/pull/151477