[llvm] StructurizeCFG: Optimize phi insertion during ssa reconstruction (PR #101301)

[via llvm-commits]

ruiling wrote:

Remove the `DeletedPhis.erase(To);` from the loop. As now we need to query leader's incoming value, which may be in a different block, we cannot erase processed block immediately.

https://github.com/llvm/llvm-project/pull/101301