Fix regression in test_langs.php

Commit 78cee358 added file Web.config to plugins and lang folder.
test_langs.php treated the file as a plugin folder and a language file.
Merge branch 'fix13-test_langs' of github.com:atrol/mantisbt into atrol-fix13-test_langs
Fix #17510: regression in test_langs.php
Backport 2e5daf7940b0eb3827bdb55e79f6f9d7759bb2ea from 2012

This removes a config option previously removed 7 years ago by 4071c8717a23db909dca4df01692f157e58344d1