use OC_DB::dropTable()

apps/files_trashbin/appinfo/update.php

@@ -5,6 +5,5 @@ $installedVersion=OCP\Config::getAppValue('files_trashbin', 'installed_version')
 if (version_compare($installedVersion, '0.6', '<')) {
 	//size of the trash bin could be incorrect, remove it for all users to
 	//enforce a recalculation during next usage.
-	$query = \OC_DB::prepare('DELETE FROM `*PREFIX*files_trashsize`');
-	$result = $query->execute();
+	\OC_DB::dropTable('files_trashsize');
 }

apps/files_versions/appinfo/update.php

@@ -3,6 +3,5 @@
 $installedVersion=OCP\Config::getAppValue('files_versions', 'installed_version');
 // move versions to new directory
 if (version_compare($installedVersion, '1.0.4', '<')) {
-	$query = \OCP\DB::prepare("DROP TABLE `*PREFIX*files_versions`");
-	$query->execute(array());
+	\OC_DB::dropTable("files_versions");
 }