Remove hard-dependency on disabled output_buffering

This removes the hard-dependency on output buffering as requested at owncloud#16013 since a lot of distributions such as Debian and Ubuntu decided to use `4096` instead of the PHP recommended and documented default value of `off`.

However, we still should encourage disabling this setting for improved performance and reliability thus the setting switches in `.user.ini` and `.htaccess` are remaining there. It is very likely that we in other cases also should disable the output buffering but aren't doing it everywhere and thus causing memory problems.

Fixes owncloud#16013

apps/files/appinfo/remote.php

@@ -30,6 +30,8 @@
 // no php execution timeout for webdav
 set_time_limit(0);
 
+// Turn off output buffering to prevent memory problems
+\OC_Util::obEnd();
 
 // Backends
 $authBackend = new \OC\Connector\Sabre\Auth();

lib/private/util.php

@@ -672,7 +672,6 @@ public static function checkServer(\OCP\IConfig $config) {
 			),
 			'ini' => [
 				'mbstring.func_overload' => 0,
-				'output_buffering' => false,
 				'default_charset' => 'UTF-8',
 			],
 		);