Remove unnecessary typename in F14Table.h (#1056)

Summary:
- Remove unneeded typename for a using alias in `F14Table.h`.
Pull Request resolved: https://github.com/facebook/folly/pull/1056

Reviewed By: nbronson

Differential Revision: D14473219

Pulled By: yfeldblum

fbshipit-source-id: a6ac26c42dbca219ce123aff00b1ee7079068007

folly/container/detail/F14Table.h

@@ -226,7 +226,7 @@ using VoidDefault =
 
 template <typename Arg, typename Default>
 using Defaulted =
-    typename std::conditional_t<std::is_same<Arg, void>::value, Default, Arg>;
+    std::conditional_t<std::is_same<Arg, void>::value, Default, Arg>;
 
 template <
     typename TableKey,