[llvm] [BOLT] Drop option --instrument-funcs-file (PR #210217)

[Paschalis Mpeis via llvm-commits]

https://github.com/paschalis-mpeis approved this pull request.

Thanks folks for the cleanup after introducing the `symbols` mode.

It would be nice if at some point we document those use cases somewhere with a small example.

https://github.com/llvm/llvm-project/pull/210217