[llvm] Revert "[CMake] Use minimum python version of 3.8 everywhere" (PR #209233)

[Aiden Grossman via llvm-commits]

boomanaiden154 wrote:

I hadn't seen that. If we're going to be adding more uses like that, I think we should just reland this as-is after branching.

https://github.com/llvm/llvm-project/pull/209233