Demo: IconTheme: Don't use deprecated builtin-icon API.
Demo: IconTheme: Don't use deprecated builtin-icon API.

By the way, there is now a separate icon browser in gtk+'s demos/.
Maybe we should create a version of that instead. I think this C++
code never corresponded to anything in the GTK+ demo.

johne53/MB3Gtkmm,GNOME/gtkmm,GNOME/gtkmm,GNOME/gtkmm,johne53/MB3Gtkmm,GNOME/gtkmm,johne53/MB3Gtkmm