[llvm] [Delinearization] Remove tryDelinearizeFixedSizeImpl (PR #169046)

[Ryotaro Kasuga via llvm-commits]

kasuga-fj wrote:

Polly uses `getIndexExpressionsFromGEP`, which is different from `tryDelinearizeFixedSizeImpl`. So this PR should not affect Polly test cases. We also should remove `getIndexExpressionsFromGEP` in the future, and it needs to update Polly test cases, which Michael is working on (https://github.com/llvm/llvm-project/pull/164798#pullrequestreview-3492677386)

https://github.com/llvm/llvm-project/pull/169046