Call XdgImportedV2Interface::send_destroyed() that takes no resource

XdgImportedV2Interface already knows what the associated resource is, so
we can call send_destroyed() method that takes no resource to let auto
generated code figure out what resource must be used. It simplifies code.

src/wayland/xdgforeign_v2_interface.cpp

@@ -239,7 +239,7 @@ void XdgImportedV2Interface::zxdg_imported_v2_destroy_resource(Resource *resourc
 
 void XdgImportedV2Interface::handleExportedDestroyed()
 {
-    send_destroyed(resource()->handle);
+    send_destroyed();
     delete this;
 }