Remove added pluginscript resource format loaders and savers on cleanup

Properly release added resource loader and save references. Otherwise PluginScript API
may cause "ObjectDB Instances still exist!" warnings and segmentation faults on exit.

modules/gdnative/pluginscript/register_types.cpp

@@ -114,6 +114,8 @@ void unregister_pluginscript_types() {
 	for (List<PluginScriptLanguage *>::Element *e = pluginscript_languages.front(); e; e = e->next()) {
 		PluginScriptLanguage *language = e->get();
 		ScriptServer::unregister_language(language);
+		ResourceLoader::remove_resource_format_loader(language->get_resource_loader());
+		ResourceSaver::remove_resource_format_saver(language->get_resource_saver());
 		memdelete(language);
 	}
 }