[libc++] Remove workaround for clang-tidy 16 in the test suite setup code (#69035)

We have moved to clang-tidy 17 now, so the workaround shouldn't be
necessary.

libcxx/utils/libcxx/test/params.py

@@ -77,9 +77,6 @@ _allStandards = ["c++03", "c++11", "c++14", "c++17", "c++20", "c++23", "c++26"]
 
 
 def getStdFlag(cfg, std):
-    # TODO(LLVM-17) Remove this clang-tidy-16 work-around
-    if std == "c++23":
-        std = "c++2b"
     if hasCompileFlag(cfg, "-std=" + std):
         return "-std=" + std
     # TODO(LLVM-19) Remove the fallbacks needed for Clang 16.