Revert "Update aosp/master libcxx rebase to r263688"

The world is burning.

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

test/libcxx/thread/futures/version.pass.cpp

@@ -1,22 +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.
-//
-//===----------------------------------------------------------------------===//
-//
-// UNSUPPORTED: libcpp-has-no-threads
-
-// <future>
-
-#include <future>
-
-#ifndef _LIBCPP_VERSION
-#error _LIBCPP_VERSION not defined
-#endif
-
-int main()
-{
-}