[llvm] [VPlan] Use vputils helper in Blend::usesFirstLaneOnly (NFC) (PR #189697)

[Andrei Elovikov via llvm-commits]

https://github.com/eas commented:

Why not just drop it and replace uses with `vputils` version? The fact that we ignore `Op` is very confusing if we keep the old interface.

https://github.com/llvm/llvm-project/pull/189697