[libsigcplusplus] signal_base: Remove unnecessary trackable.h include.

[Murray Cumming <murrayc src gnome org>]

commit f55bdf9b8980ef5914d7f0f939c7292cbe302495
Author: Murray Cumming <murrayc murrayc com>
Date:   Thu Apr 28 12:59:44 2016 +0200

    signal_base: Remove unnecessary trackable.h include.

 sigc++/signal_base.h |    1 -
 1 files changed, 0 insertions(+), 1 deletions(-)
---
diff --git a/sigc++/signal_base.h b/sigc++/signal_base.h
index 90fca8a..bcff3aa 100644
--- a/sigc++/signal_base.h
+++ b/sigc++/signal_base.h
@@ -24,7 +24,6 @@
 #include <memory> //For std::shared_ptr<>
 #include <sigc++config.h>
 #include <sigc++/type_traits.h>
-#include <sigc++/trackable.h>
 #include <sigc++/functors/slot.h>
 #include <sigc++/functors/mem_fun.h>