listbox: remove css hack to add separator
Back in the day, there were no bindings for gtk_listbox_set_header_func, so we worked around it with some css.
Now though we can use the header_func and do it properly.
Back in the day, there were no bindings for gtk_listbox_set_header_func, so we worked around it with some css.
Now though we can use the header_func and do it properly.