N°2651 rollback gitignore for lib tests dirs

Too dangerous ! We'll work properly on this but for 2.8

lib/symfony/debug/Tests/Fixtures/DeprecatedClass.php

@@ -0,0 +1,12 @@
+<?php
+
+namespace Symfony\Component\Debug\Tests\Fixtures;
+
+/**
+ * @deprecated but this is a test
+ *             deprecation notice
+ * @foobar
+ */
+class DeprecatedClass
+{
+}