[libsigcplusplus] Remove another unecessary c++ marker comment.

[Murray Cumming <murrayc src gnome org>]

commit da879d986811341101c7d64dc819f532f1ffdcc4
Author: Murray Cumming <murrayc murrayc com>
Date:   Wed Apr 20 09:11:35 2016 +0200

    Remove another unecessary c++ marker comment.

 tests/test_bind_refptr.cc |    1 -
 1 files changed, 0 insertions(+), 1 deletions(-)
---
diff --git a/tests/test_bind_refptr.cc b/tests/test_bind_refptr.cc
index 202baf3..062cb7d 100644
--- a/tests/test_bind_refptr.cc
+++ b/tests/test_bind_refptr.cc
@@ -29,7 +29,6 @@
 
 #define ACTIVATE_BUG 1
 
-// -*- c++ -*-
 #ifndef _GLIBMM_REFPTR_H
 #define _GLIBMM_REFPTR_H