Moved the PSR-4 namespaced test directory to the correct folder

I know this probably doesn't belong in this PR, but it has been thoroughly discussed and I don't think anyone will mind :)

composer.json

@@ -45,7 +45,7 @@
   },
   "autoload-dev": {
     "psr-4": {
-      "Automattic\\WooCommerce\\Tests\\": "tests/php/"
+      "Automattic\\WooCommerce\\Tests\\": "tests/php/src"
     }
   },
   "scripts": {

tests/php/includes/admin/helper/class-wc-helper-test.php

@@ -5,12 +5,10 @@
  * @package WooCommerce|Tests|WC_Helper.
  */
 
-namespace Automattic\WooCommerce;
-
 /**
  * Class WC_Tests_WC_Helper.
  */
-class WCHelperTest extends \WC_Unit_Test_Case {
+class WC_Helper_Test extends \WC_Unit_Test_Case {
 
 	/**
 	 * Test that woo plugins are loaded correctly even if incorrect cache is intially set.