[gn build] Port f041b34

Author: llvmgnsyncbot

llvm/utils/gn/secondary/libcxx/include/BUILD.gn

@@ -607,7 +607,6 @@ if (current_toolchain == default_toolchain) {
       "__pstl/internal/parallel_backend_tbb.h",
       "__pstl/internal/parallel_backend_utils.h",
       "__pstl/internal/parallel_impl.h",
-      "__pstl/internal/pstl_config.h",
       "__pstl/internal/unseq_backend_simd.h",
       "__pstl/internal/utils.h",
       "__random/bernoulli_distribution.h",