[gtkmm] TreeView: Remove an obsolete comment

[Daniel Boles <dboles src gnome org>]

commit eb11f2082abb4e781dc4c831854b632f2e2938f2
Author: Daniel Boles <dboles src gmail com>
Date:   Wed May 10 16:10:34 2017 +0100

    TreeView: Remove an obsolete comment
    
    Commit 4504487c7 replaced the old C syntax (void*)0 with nullptr but did
    not remove this comment, which referred to the original cast expression.

 gtk/src/treeview.ccg |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
---
diff --git a/gtk/src/treeview.ccg b/gtk/src/treeview.ccg
index e22f95b..83e3679 100644
--- a/gtk/src/treeview.ccg
+++ b/gtk/src/treeview.ccg
@@ -201,7 +201,7 @@ bool TreeView::get_path_at_pos(int x, int y, TreeModel::Path& path) const
 int TreeView::insert_column(const Glib::ustring& title, CellRenderer& cell, int position)
 {
   return gtk_tree_view_insert_column_with_attributes(
-      gobj(), position, const_cast<char*>(title.c_str()), cell.gobj(), nullptr); //Note that some compilers 
need the extra (void*) clue.
+      gobj(), position, const_cast<char*>(title.c_str()), cell.gobj(), nullptr);
 }
 
 int TreeView::append_column(const Glib::ustring& title, CellRenderer& cell)