Remove redundant void from C++ sources (#1486)

diff --git a/src/hb-buffer-serialize.cc b/src/hb-buffer-serialize.cc
index 343ae1c..6e265e8 100644
--- a/src/hb-buffer-serialize.cc
+++ b/src/hb-buffer-serialize.cc
@@ -44,7 +44,7 @@
  * Since: 0.9.7
  **/
 const char **
-hb_buffer_serialize_list_formats (void)
+hb_buffer_serialize_list_formats ()
 {
   return serialize_formats;
 }