[clang] [clang][Analyzer][NFC] Simplify preDefault/preFseek/preFreadFwrite of StreamChecker (PR #71394)

[Balazs Benics via cfe-commits]

https://github.com/steakhal requested changes to this pull request.

I find this alternative less idiomatic (dissimilar to how we implement checks in other checkers), thus I find this less readable.
I'm okay with that amount of redundancy as it was present.

https://github.com/llvm/llvm-project/pull/71394