user-accounts: Do not access already removed toolbar

Commit eb9c1106 removed add-remove-toolbar, however, some leftovers are
in the code which causes the following errors:
Gtk-CRITICAL **: gtk_widget_get_style_context: assertion 'GTK_IS_WIDGET (widget)' failed
Gtk-CRITICAL **: gtk_style_context_set_junction_sides: assertion 'GTK_IS_STYLE_CONTEXT (context)' failed

https://bugzilla.gnome.org/show_bug.cgi?id=767065