[llvm] [BOLT][NFC] Simplify getSplitSymbolName (PR #88619)

[Amir Ayupov via llvm-commits]

aaupov wrote:

> Honestly this doesn't seem to me such of a simplification. I liked the previous version better. The number of lines of code added is also the same as the number removed.

It was intended to be a preparation for https://github.com/llvm/llvm-project/pull/88627, but we're not moving forward with this approach to handle split fragments.

https://github.com/llvm/llvm-project/pull/88619