[llvm] [CallGraphUpdater] Remove some legacy pass manager support (PR #98362)

[Arthur Eubanks via llvm-commits]

aeubanks wrote:

the legacy PM version of `CallGraphUpdater::initialize()` is never called, so all the legacy PM infra in CallGraphUpdater can be deleted. that makes some of the CallGraphUpdater methods empty, so we can delete them and any callers

https://github.com/llvm/llvm-project/pull/98362