[llvm] [VectorCombine] Remove requirement for Instructions in shuffleToIdentity (PR #93543)

[via llvm-commits]

ronlieb wrote:

@davemgreen   we noticed a regression in two of our hip tests that seemed to be caused by this patch.
dont have a reproducer as of now. reporting it now. we will work on a test case , might take a day or two  on our end.

https://github.com/llvm/llvm-project/pull/93543