Revert "Merge to upstream r304942."

This reverts commit 83b1388ecd, reversing
changes made to f20819f925.

Test: treehugger
Bug: None

test/std/strings/basic.string/traits_mismatch.fail.cpp

@@ -1,18 +0,0 @@
-//===----------------------------------------------------------------------===//
-//
-//                     The LLVM Compiler Infrastructure
-//
-// This file is dual licensed under the MIT and the University of Illinois Open
-// Source Licenses. See LICENSE.TXT for details.
-//
-//===----------------------------------------------------------------------===//
-
-// <string>
-//   The strings's value type must be the same as the traits's char_type
-
-#include <string>
-
-int main()
-{
-    std::basic_string<char, std::char_traits<wchar_t>> s;
-}