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

[Younan Zhang via cfe-commits]

zyn0217 wrote:

(I presume you don't have commit access, so I'll help you merge it. Next time, please add an "NFC" term to the commit title if the PR doesn't contain any functional changes.)

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