[llvm] [InstCombine] Remove redundant shift folds (NFCI) (PR #90016)

[Yingwei Zheng via llvm-commits]

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

LGTM. They are unreachable in practice:

https://dtcxzyw.github.io/llvm-opt-benchmark/coverage/home/dtcxzyw/llvm-project/llvm/lib/Transforms/InstCombine/InstCombineShifts.cpp.html#L1123

https://dtcxzyw.github.io/llvm-opt-benchmark/coverage/home/dtcxzyw/llvm-project/llvm/lib/Transforms/InstCombine/InstCombineShifts.cpp.html#L1398

https://github.com/llvm/llvm-project/pull/90016