[llvm] RISCV: Use hasOneNonDBGUse instead of kill flag for cascaded select (PR #228940)

[Matt Arsenault via llvm-commits]

arsenm wrote:

> > Avoid depending on the kill flag which will not be set in the future.
> 
> What's the change causing this?
> 

Removal of kill flags. They've been deprecated for well over a decade and are a LiveVariables thing. 


https://github.com/llvm/llvm-project/pull/228940