[llvm] IR: Remove null UseList checks in hasNUses methods (PR #165929)

[Matt Arsenault via llvm-commits]

arsenm wrote:

> Was called and I believe `Op` became Constant after instcombine pass. Didn't have a chance to do a closer check though so it might be something on our end.

You shouldn't rely on the use lists of ConstantData. We still tolerate use_empty checks on them, mostly because there's just too much code to fix at a time


https://github.com/llvm/llvm-project/pull/165929