[llvm] [BOLT][NFC] Refactor function state check (PR #73420)

[Maksim Panchenko via llvm-commits]

maksfb wrote:

> Just for my understanding: we were testing the conditions used for emission rather than the actual emitted state of BF, and this diff fixes it, right? Which cases did we miss where the function was simple but wasn't emitted?

This PR is pure NFC to improve readability. Actually, @ShatianWang pointed out that the same check is executed at the beginning of the function. I.e. the check is redundant and I'm going to remove it.

https://github.com/llvm/llvm-project/pull/73420