[libsigcplusplus] adaptor_trait: Remove an apparently-unnecessary extra declaration for Doxygen.

[Murray Cumming <murrayc src gnome org>]

commit d63dd840cff6ab8b78798760c8712cbad2e66c36
Author: Murray Cumming <murrayc murrayc com>
Date:   Wed Apr 13 20:27:23 2016 +0200

    adaptor_trait: Remove an apparently-unnecessary extra declaration for Doxygen.

 sigc++/adaptors/adaptor_trait.h |    8 +-------
 1 files changed, 1 insertions(+), 7 deletions(-)
---
diff --git a/sigc++/adaptors/adaptor_trait.h b/sigc++/adaptors/adaptor_trait.h
index 049c68e..c6d5a86 100644
--- a/sigc++/adaptors/adaptor_trait.h
+++ b/sigc++/adaptors/adaptor_trait.h
@@ -136,15 +136,9 @@ struct visitor<adaptor_functor<T_functor>>
  *
  * @ingroup adaptors
  */
-#ifndef DOXYGEN_SHOULD_SKIP_THIS
 template <class T_functor, bool I_isadaptor = std::is_base_of<adaptor_base, T_functor>::value>
 struct adaptor_trait;
-#else
-template <class T_functor, bool I_isadaptor = std::is_base_of<adaptor_base, T_functor>::value>
-struct adaptor_trait
-{
-};
-#endif
+
 
 /** Trait that specifies what is the adaptor version of a functor type.
  * This template specialization is used for types that inherit from adaptor_base.