Use public IAppManager instead of OC_App

Signed-off-by: Carl Schwan <carl@carlschwan.eu>

apps/dav/lib/Connector/Sabre/Directory.php

@@ -255,7 +255,7 @@ class Directory extends \OCA\DAV\Connector\Sabre\Node implements \Sabre\DAV\ICol
 			if (!$this->info->isReadable()) {
 				// return 403 instead of 404 because a 404 would make
 				// the caller believe that the collection itself does not exist
-				if (\OC_App::isEnabled('files_accesscontrol')) {
+				if (\OCP\Server::get(\OCP\App\IAppManager::class)->isInstalled('files_accesscontrol')) {
 					throw new Forbidden('No read permissions. This might be caused by files_accesscontrol, check your configured rules');
 				} else {
 					throw new Forbidden('No read permissions');