Revert "Update aosp/master libcxx rebase to r263688"

The world is burning.

This reverts commit c004fd909c, reversing
changes made to 1418e4163d.

test/libcxx/extensions/hash/specializations.fail.cpp

@@ -1,17 +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.
-//
-//===----------------------------------------------------------------------===//
-
-#include <assert.h>
-#include <ext/hash_map>
-#include <string>
-
-int main()
-{
-    assert(__gnu_cxx::hash<std::string>()(std::string()) == 0);  // error
-}