Move select2 from files_external to core

apps/files_external/settings.php

@@ -25,8 +25,8 @@ OC_Util::checkAdminUser();
 OCP\Util::addScript('files_external', 'settings');
 OCP\Util::addStyle('files_external', 'settings');
 
-OCP\Util::addScript('files_external', '../3rdparty/select2/select2');
-OCP\Util::addStyle('files_external', '../3rdparty/select2/select2');
+OCP\Util::addScript('core', 'select2/select2');
+OCP\Util::addStyle('core', 'select2/select2');
 
 $backends = OC_Mount_Config::getBackends();
 $personal_backends = array();