Revert previous "fix" it introduces new issues of its own.

The problem that's causing us to lose windows is that rapid hiding and
unhiding causes a backlog of X events, so we lose track of client state,
and delete cc->pwin when we should not. A proper fix will arrive when it's been
worked out.

xevents.c

@@ -70,7 +70,7 @@ xev_handle_unmapnotify(struct xevent *xev, XEvent *ee)
 	struct client_ctx *cc;
 
 	if ((cc = client_find(e->window)) != NULL)
-		xu_setstate(cc, WithdrawnState);
+		client_delete(cc, e->send_event, 0);
 
 	xev_register(xev);
 }