[llvm] RISCV: Stop setting kill flags on virtual registers before FinalizeISel (PR #229013)

[Matt Arsenault via llvm-commits]

arsenm wrote:

I'm only able to trigger MachineLICM based on a kill flag in cases with multiple uses where SelectionDAG wouldn't have introduced a kill flag to start with, such that it only happens with hand written MIR 

https://github.com/llvm/llvm-project/pull/229013