[ASTMatchers] Simplify isDefaultedHelper (NFC)#137571

kazutakahirata merged 2 commits intollvm:mainllvm/llvm-project:mainfrom

kazutakahirata:cleanup_001_constexpr_if_clang_ASTMatcherskazutakahirata/llvm-project:cleanup_001_constexpr_if_clang_ASTMatchersCopy head branch name to clipboard