client_focus_update(): Balance the lua stack

There is a push 15 lines before the push that is removed here, but the client
that is pushed there was never popped. Bad.

Fix this by letting luaA_class_emit_signal() do the needed pop for us.

Signed-off-by: Uli Schlachter <psychon@znc.in>
Signed-off-by: Julien Danjou <julien@danjou.info>

client.c

@@ -431,7 +431,6 @@ client_focus_update(client_t *c)
         luaA_dofunction_from_registry(globalconf.L, globalconf.hooks.focus, 1, 0);
     }
 
-    luaA_object_push(globalconf.L, c);
     luaA_class_emit_signal(globalconf.L, &client_class, "focus", 1);
 }