Revert "Update aosp/master libcxx rebase to r263688"

The world is burning.

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

test/libcxx/utilities/time/date.time/localtime.thread-unsafe.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.
-//
-//===----------------------------------------------------------------------===//
-
-// REQUIRES: libcpp-has-no-thread-unsafe-c-functions
-
-#include <ctime>
-
-int main() {
-    // localtime is not thread-safe.
-    std::time_t t = 0;
-    std::localtime(&t);
-}