[gn] port 118f120

Author: nico

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

@@ -996,7 +996,6 @@ if (current_toolchain == default_toolchain) {
       "exception",
       "execution",
       "expected",
-      "experimental/__config",
       "experimental/__simd/aligned_tag.h",
       "experimental/__simd/declaration.h",
       "experimental/__simd/reference.h",