[llvm] Remove unused standard header inclusion: <iterator>, <utility>, <type_traits> (PR #167318)

[Jonas Devlieghere via llvm-commits]

JDevlieghere wrote:

Can you please motivate this change? This feels like a "large-scale change of existing code" that's explicitly [discouraged](https://llvm.org/docs/CodingStandards.html#introduction) and/or an extractive contribution, especially for those having to merge this downstream. I'm not necessarily pushing back, I just down know without a PR description.

https://github.com/llvm/llvm-project/pull/167318