[libsigcplusplus] adaptor_trait: Remove unused functor_type.

[Murray Cumming <murrayc src gnome org>]

commit 9307f61b4be827c152a045e46e3b248b6a9dad5c
Author: Murray Cumming <murrayc murrayc com>
Date:   Wed Apr 13 13:18:37 2016 +0200

    adaptor_trait: Remove unused functor_type.

 sigc++/adaptors/adaptor_trait.h |    6 ++++--
 1 files changed, 4 insertions(+), 2 deletions(-)
---
diff --git a/sigc++/adaptors/adaptor_trait.h b/sigc++/adaptors/adaptor_trait.h
index 2c7dda2..049c68e 100644
--- a/sigc++/adaptors/adaptor_trait.h
+++ b/sigc++/adaptors/adaptor_trait.h
@@ -154,7 +154,6 @@ template <class T_functor>
 struct adaptor_trait<T_functor, true>
 {
   using result_type = typename T_functor::result_type;
-  using functor_type = T_functor;
   using adaptor_type = T_functor;
 };
 
@@ -167,8 +166,11 @@ struct adaptor_trait<T_functor, true>
 template <class T_functor>
 struct adaptor_trait<T_functor, false>
 {
-  using result_type = typename functor_trait<T_functor>::result_type;
+private:
   using functor_type = typename functor_trait<T_functor>::functor_type;
+
+public:
+  using result_type = typename functor_trait<T_functor>::result_type;
   using adaptor_type = adaptor_functor<functor_type>;
 };