[llvm] [Support] Erase blocks after DomTree::eraseNode (PR #101195)

[Alexis Engelke via llvm-commits]

aengelke wrote:

I could do that, but I'd rather land #101198 afterwards, where an assertion about the parent is added to getNode(), which is called by eraseNode.

https://github.com/llvm/llvm-project/pull/101195