Remove deprecation from then that simply forwards to thenTry. Deprecation was...

Remove deprecation from then that simply forwards to thenTry. Deprecation was inconsistent with defer.

Summary: Future::then that forwards directly to thenTry is to be left for compatibility with Future::defer and to keep naming simple. This removes the confusing deprecation warning.

Reviewed By: yfeldblum

Differential Revision: D15057215

fbshipit-source-id: 84103e47c958f1db602804f625591ba899e98b23

folly/futures/Future.h

@@ -1119,12 +1119,8 @@ class Future : private futures::detail::FutureBase<T> {
   /// - Calling code should act as if `valid() == false`,
   ///   i.e., as if `*this` was moved into RESULT.
   /// - `RESULT.valid() == true`
-  /// NOTE: All three of these variations are deprecated and deprecation
-  /// attributes will be added in the near future. Please prefer thenValue,
-  /// thenTry or thenError rather than then and onError as they avoid ambiguity
-  /// when using polymorphic lambdas.
   template <typename F, typename R = futures::detail::callableResult<T, F>>
-  [[deprecated("ERROR: use thenTry instead")]] typename std::enable_if<
+  typename std::enable_if<
       !is_invocable<F, T&&>::value && !is_invocable<F>::value,
       typename R::Return>::type
   then(F&& func) && {