Revert r344529 "Implement the first part of the calendar support for C++20"

Revert r344535 "Wrap up the new chrono literals in an #ifdef..."
Revert r344546 "Mark a couple of test cases as 'C++17-only'..."

Some of the buildbot failures were masked by another error,
and this one was probably missed.


git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@344580 91177308-0d34-0410-b5e6-96231b3b80d8

test/std/utilities/time/months.pass.cpp

@@ -1,29 +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: c++03, c++11, c++14, c++17
-
-// <chrono>
-
-// using months = duration<signed integer type of at least 20 bits, ratio_divide<years::period, ratio<12>>>;
-
-
-#include <chrono>
-#include <type_traits>
-#include <limits>
-
-int main()
-{
-    typedef std::chrono::months D;
-    typedef D::rep Rep;
-    typedef D::period Period;
-    static_assert(std::is_signed<Rep>::value, "");
-    static_assert(std::is_integral<Rep>::value, "");
-    static_assert(std::numeric_limits<Rep>::digits >= 20, "");
-    static_assert(std::is_same_v<Period, std::ratio_divide<std::chrono::years::period, std::ratio<12>>>, "");
-}