Rm unused proprocessor block

Summary: This preprocessor block is old and outdated. Per V1 of this diff, no one uses the else branch. Remove it.

Reviewed By: yfeldblum, Orvid

Differential Revision: D52662418

fbshipit-source-id: 51ca4f39b0d3a6db5958081224540601e7251aae

folly/Chrono.h

@@ -25,155 +25,13 @@
 #include <folly/lang/Exception.h>
 #include <folly/portability/Time.h>
 
-/***
- *  include or backport:
- *  * std::chrono::ceil
- *  * std::chrono::floor
- *  * std::chrono::round
- */
-
-#if __cpp_lib_chrono >= 201510 || _LIBCPP_STD_VER > 14 || _MSC_VER
-
 namespace folly {
 namespace chrono {
 
 /* using override */ using std::chrono::abs;
 /* using override */ using std::chrono::ceil;
 /* using override */ using std::chrono::floor;
 /* using override */ using std::chrono::round;
-} // namespace chrono
-} // namespace folly
-
-#else
-
-namespace folly {
-namespace chrono {
-
-namespace detail {
-
-//  from: http://en.cppreference.com/w/cpp/chrono/duration/ceil, CC-BY-SA
-template <typename T>
-struct is_duration : std::false_type {};
-template <typename Rep, typename Period>
-struct is_duration<std::chrono::duration<Rep, Period>> : std::true_type {};
-
-template <typename To, typename Duration>
-constexpr To ceil_impl(Duration const& d, To const& t) {
-  return t < d ? t + To{1} : t;
-}
-
-template <typename To, typename Duration>
-constexpr To floor_impl(Duration const& d, To const& t) {
-  return t > d ? t - To{1} : t;
-}
-
-template <typename To, typename Diff>
-constexpr To round_impl(To const& t0, To const& t1, Diff diff0, Diff diff1) {
-  return diff0 < diff1 ? t0 : diff1 < diff0 ? t1 : t0.count() & 1 ? t1 : t0;
-}
-
-template <typename To, typename Duration>
-constexpr To round_impl(Duration const& d, To const& t0, To const& t1) {
-  return round_impl(t0, t1, d - t0, t1 - d);
-}
-
-template <typename To, typename Duration>
-constexpr To round_impl(Duration const& d, To const& t0) {
-  return round_impl(d, t0, t0 + To{1});
-}
-} // namespace detail
-
-//  mimic: std::chrono::abs, C++17
-template <
-    typename Rep,
-    typename Period,
-    typename = typename std::enable_if<
-        std::chrono::duration<Rep, Period>::min() <
-        std::chrono::duration<Rep, Period>::zero()>::type>
-constexpr std::chrono::duration<Rep, Period> abs(
-    std::chrono::duration<Rep, Period> const& d) {
-  return d < std::chrono::duration<Rep, Period>::zero() ? -d : d;
-}
-
-//  mimic: std::chrono::ceil, C++17
-//  from: http://en.cppreference.com/w/cpp/chrono/duration/ceil, CC-BY-SA
-template <
-    typename To,
-    typename Rep,
-    typename Period,
-    typename = typename std::enable_if<detail::is_duration<To>::value>::type>
-constexpr To ceil(std::chrono::duration<Rep, Period> const& d) {
-  return detail::ceil_impl(d, std::chrono::duration_cast<To>(d));
-}
-
-//  mimic: std::chrono::ceil, C++17
-//  from: http://en.cppreference.com/w/cpp/chrono/time_point/ceil, CC-BY-SA
-template <
-    typename To,
-    typename Clock,
-    typename Duration,
-    typename = typename std::enable_if<detail::is_duration<To>::value>::type>
-constexpr std::chrono::time_point<Clock, To> ceil(
-    std::chrono::time_point<Clock, Duration> const& tp) {
-  return std::chrono::time_point<Clock, To>{ceil<To>(tp.time_since_epoch())};
-}
-
-//  mimic: std::chrono::floor, C++17
-//  from: http://en.cppreference.com/w/cpp/chrono/duration/floor, CC-BY-SA
-template <
-    typename To,
-    typename Rep,
-    typename Period,
-    typename = typename std::enable_if<detail::is_duration<To>::value>::type>
-constexpr To floor(std::chrono::duration<Rep, Period> const& d) {
-  return detail::floor_impl(d, std::chrono::duration_cast<To>(d));
-}
-
-//  mimic: std::chrono::floor, C++17
-//  from: http://en.cppreference.com/w/cpp/chrono/time_point/floor, CC-BY-SA
-template <
-    typename To,
-    typename Clock,
-    typename Duration,
-    typename = typename std::enable_if<detail::is_duration<To>::value>::type>
-constexpr std::chrono::time_point<Clock, To> floor(
-    std::chrono::time_point<Clock, Duration> const& tp) {
-  return std::chrono::time_point<Clock, To>{floor<To>(tp.time_since_epoch())};
-}
-
-//  mimic: std::chrono::round, C++17
-//  from: http://en.cppreference.com/w/cpp/chrono/duration/round, CC-BY-SA
-template <
-    typename To,
-    typename Rep,
-    typename Period,
-    typename = typename std::enable_if<
-        detail::is_duration<To>::value &&
-        !std::chrono::treat_as_floating_point<typename To::rep>::value>::type>
-constexpr To round(std::chrono::duration<Rep, Period> const& d) {
-  return detail::round_impl(d, floor<To>(d));
-}
-
-//  mimic: std::chrono::round, C++17
-//  from: http://en.cppreference.com/w/cpp/chrono/time_point/round, CC-BY-SA
-template <
-    typename To,
-    typename Clock,
-    typename Duration,
-    typename = typename std::enable_if<
-        detail::is_duration<To>::value &&
-        !std::chrono::treat_as_floating_point<typename To::rep>::value>::type>
-constexpr std::chrono::time_point<Clock, To> round(
-    std::chrono::time_point<Clock, Duration> const& tp) {
-  return std::chrono::time_point<Clock, To>{round<To>(tp.time_since_epoch())};
-}
-} // namespace chrono
-} // namespace folly
-
-#endif
-
-namespace folly {
-namespace chrono {
 
 //  steady_clock_spec
 //