[llvm] InstSimplify: strip bad TODO (NFC) (PR #92754)

[Matt Arsenault via llvm-commits]

arsenm wrote:

> foldIdentityShuffles() has a TODO comment about looking through bitcasts. Looking through any intervening instructions when folding shuffles is out-of-scope of InstructionSimplify, as the analysis is not allowed to modify the IR in any way. Strip this bad TODO.

You can look through intervening instructions, you just can't introduce new instructions. You can still probably manage a restricted subset of what you were trying to do but I didn't look that closely 

https://github.com/llvm/llvm-project/pull/92754