[clang] [Clang][Sema] Remove duplicate check in if-condition (PR #101070)

[Younan Zhang via cfe-commits]

https://github.com/zyn0217 approved this pull request.

Thanks.
(However I'm not an OpenMP maintainer, but since this PR is clearly an NFC change, I'd boldly approve it.)

https://github.com/llvm/llvm-project/pull/101070