Fix 'make check' after Gtk::Arrow has been deprecated

* examples/Makefile.am: Delete examples/others/arrow/direction.
* examples/others/arrow/arrow.cc: Delete this file, rename direction.cc
to arrow.cc, and use Gtk::Button::set_image_from_icon_name() instead of
Gtk::Arrow.
* examples/others/arrow/direction.cc: Rename to arrow.cc.
* examples/others/cellrenderercustom/popupentry.cc:
Use Gtk::Button::set_image_from_icon_name() instead of Gtk::Arrow.