Remove extraneous uses of keyword typename in fibers collectN

Summary: [Folly] Remove extraneous uses of keyword `typename` in fibers `collectN`.

Reviewed By: ericniebler

Differential Revision: D14317102

fbshipit-source-id: 1ae04081258bf2398865a1cc5461618648623158

folly/fibers/WhenN-inl.h

@@ -27,7 +27,7 @@ typename std::enable_if<
         invoke_result_t<
             typename std::iterator_traits<InputIterator>::value_type>,
         void>::value,
-    typename std::vector<typename std::pair<
+    std::vector<std::pair<
         size_t,
         invoke_result_t<
             typename std::iterator_traits<InputIterator>::value_type>>>>::type

folly/fibers/WhenN.h

@@ -44,7 +44,7 @@ typename std::enable_if<
         invoke_result_t<
             typename std::iterator_traits<InputIterator>::value_type>,
         void>::value,
-    typename std::vector<typename std::pair<
+    std::vector<std::pair<
         size_t,
         invoke_result_t<
             typename std::iterator_traits<InputIterator>::value_type>>>>::