simplify some channel test helpers

Summary:
* Simplify template specs.
* Use C++17 param-pack folds in place of the C++11 param-pack expansion-into-array trick.

Reviewed By: dmm-fb

Differential Revision: D52875149

fbshipit-source-id: 81e3b2873ac050c9cac9708f47cabc7c259c962f

folly/experimental/channels/test/ChannelTestUtil.h

@@ -30,18 +30,16 @@ template <typename T, typename... Others>
 std::vector<T> toVector(T firstItem, Others... items) {
   std::vector<T> itemsVector;
   itemsVector.push_back(std::move(firstItem));
-  [[maybe_unused]] int dummy[] = {
-      (itemsVector.push_back(std::move(items)), 0)...};
+  (void(itemsVector.push_back(std::move(items))), ...);
   return itemsVector;
 }
 
-template <typename TPair, typename... Others>
-folly::F14FastMap<typename TPair::first_type, typename TPair::second_type>
-toMap(TPair firstPair, Others... items) {
-  folly::F14FastMap<typename TPair::first_type, typename TPair::second_type>
-      itemsMap;
+template <typename Key, typename Mapped, typename... Others>
+folly::F14FastMap<std::remove_const_t<Key>, Mapped> toMap(
+    std::pair<Key, Mapped> firstPair, Others... items) {
+  folly::F14FastMap<std::remove_const_t<Key>, Mapped> itemsMap;
   itemsMap.insert(std::move(firstPair));
-  [[maybe_unused]] int dummy[] = {(itemsMap.insert(std::move(items)), 0)...};
+  (void(itemsMap.insert(std::move(items))), ...);
   return itemsMap;
 }