[libsigcplusplus] compose: Remove left-over adaptor_type.

[Murray Cumming <murrayc src gnome org>]

commit c267f66ab15ae2463eea951aee29a73ba60cabce
Author: Murray Cumming <murrayc murrayc com>
Date:   Wed Apr 13 22:35:10 2016 +0200

    compose: Remove left-over adaptor_type.

 sigc++/adaptors/compose.h |    4 ----
 1 files changed, 0 insertions(+), 4 deletions(-)
---
diff --git a/sigc++/adaptors/compose.h b/sigc++/adaptors/compose.h
index 79a94dc..c261b7b 100644
--- a/sigc++/adaptors/compose.h
+++ b/sigc++/adaptors/compose.h
@@ -77,10 +77,6 @@ struct compose1_functor : public adapts<T_setter>
 template <class T_setter, class T_getter1, class T_getter2>
 struct compose2_functor : public adapts<T_setter>
 {
-private:
-  using adaptor_type = typename adapts<T_setter>::adaptor_type;
-
-public:
   decltype(auto) operator()() { return this->functor_(get1_(), get2_()); }
 
   template <class... T_arg>