Resize grips have been removed as of Gtk+ 3.14

The documentation at [1] says:

    gtk_window_set_has_resize_grip has been deprecated since version
    3.14 and should not be used in newly-written code. Resize grips have
    been removed.

[1] https://developer.gnome.org/gtk3/stable/GtkWindow.html#gtk-window-set-has-resize-grip