[llvm] [StackColoring] Delete dead stack slots (PR #72633)

[Piotr Sobczak via llvm-commits]

piotrAMD wrote:

> @piotrAMD What's the failing test?

 LLVM :: DebugInfo/COFF/lexicalblock.ll
 
 Also visible here: https://buildkite.com/llvm-project/github-pull-requests/builds/22410#018c633f-a0f4-4604-8c7d-17deb1708815

https://github.com/llvm/llvm-project/pull/72633