editor: don't remove unsubscribed handlers in eap-method-leap/eap-method-simple

During destroy of the security dialogs EAPMethodSimple and
EAPMethodLEAP, the handlers are unsubscribed from the widget.

Remove the unsubscription of 'wireless_security_changed_cb', because
this function is actually never subscribed to the widget.

Signed-off-by: Thomas Haller <thaller@redhat.com>
editor: initialize the destroy handler at last in eap_method_init/wireless_security_init

When 'eap_method_init' or 'wireless_security_init' fails to read the
UI xml file, it calls 'eap_method_unref' or 'wireless_security_unref',
respectively. The unref methods call the destroy handler, but they
should not do it in this case, because the objects were not fully
constructed.

Fix this, be setting the destroy handler only at the end of
the init methods.

Signed-off-by: Thomas Haller <thaller@redhat.com>