[llvm] [NFC] Various Cleanup in StackColoring, StackSlotColoring, LiveStacks (PR #143931)

[Matt Arsenault via llvm-commits]

arsenm wrote:

> It seems like there was no consensus to always deleting lifetime annotations in StackColoring. so I removed that commit.

It might be a good idea but not as part of this patch, that's much more potentially load bearing than the rest of the cleanups here 



https://github.com/llvm/llvm-project/pull/143931