Move remove_reference_wrapper to coro traits

Summary: [Folly] Move remove_reference_wrapper to coro traits, since this is not a language-level trait and is there to be used in the coro library.

Reviewed By: iahs

Differential Revision: D20301017

fbshipit-source-id: aa78488cc5138e6ade9dcbc99ec1b75b65c74c78

folly/Traits.h

@@ -240,20 +240,6 @@ struct remove_cvref {
 template <typename T>
 using remove_cvref_t = typename remove_cvref<T>::type;
 
-/**
- * A type trait to unwrap a std::reference_wrapper<T> to a type T
- */
-template <typename T>
-struct remove_reference_wrapper {
-  using type = T;
-};
-template <typename T>
-struct remove_reference_wrapper<std::reference_wrapper<T>> {
-  using type = T;
-};
-template <typename T>
-using remove_reference_wrapper_t = typename remove_reference_wrapper<T>::type;
-
 namespace detail {
 template <typename Src>
 struct like_ {

folly/experimental/coro/Traits.h

@@ -24,6 +24,20 @@
 namespace folly {
 namespace coro {
 
+/**
+ * A type trait to unwrap a std::reference_wrapper<T> to a type T
+ */
+template <typename T>
+struct remove_reference_wrapper {
+  using type = T;
+};
+template <typename T>
+struct remove_reference_wrapper<std::reference_wrapper<T>> {
+  using type = T;
+};
+template <typename T>
+using remove_reference_wrapper_t = typename remove_reference_wrapper<T>::type;
+
 namespace detail {
 
 template <typename T>