[libsigcplusplus] signal: Remove public emitter_type alias.

[Murray Cumming <murrayc src gnome org>]

commit b99a3f7ea1e45219bf6c543acd8b766103e64710
Author: Murray Cumming <murrayc murrayc com>
Date:   Thu Apr 21 14:02:27 2016 +0200

    signal: Remove public emitter_type alias.

 sigc++/signal.h |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
---
diff --git a/sigc++/signal.h b/sigc++/signal.h
index 0118c9f..71340b0 100644
--- a/sigc++/signal.h
+++ b/sigc++/signal.h
@@ -616,7 +616,6 @@ template <typename T_return, typename T_accumulator, typename... T_arg>
 class signal_with_accumulator : public signal_base
 {
 public:
-  using emitter_type = internal::signal_emit<T_return, T_accumulator, T_arg...>;
   using slot_type = slot<T_return(T_arg...)>;
   using connection = slot_iterator<slot_type>;
 
@@ -668,6 +667,7 @@ public:
    */
   decltype(auto) emit(type_trait_take_t<T_arg>... a) const
   {
+    using emitter_type = internal::signal_emit<T_return, T_accumulator, T_arg...>;
     return emitter_type::emit(impl_, a...);
   }