[Codegen] Make sure kill flags are not incorrect from removed machine phi's

We need to clear the kill flags on both SingleValReg and OldReg, to ensure they remain
conservatively correct.

Differential Revision: https://reviews.llvm.org/D58114


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@353847 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed