Revert "core: don't leak ActiveConnection object on AddAndActivate failure"

This reverts commit 8b6a1ac62f.

Original patch was in error; 'active' is already gs_unref_object.

src/nm-manager.c

@@ -3469,7 +3469,6 @@ activation_add_done (NMSettings *settings,
 	                            FALSE,
 	                            nm_active_connection_get_subject (active),
 	                            error->message);
-	g_object_unref (active);
 	g_clear_error (&local);
 }