Fixed final php code style warning

The solution is a bit worse than the original hack, but php-cs-fixer now
reports the original solution as error. Therefore, to avoid the 'unused
parameter' warning by the constructor, we now save it in a private
variable shortly.

Author: Sebb767

src/Resource/ArraySystemProperties.php

@@ -13,14 +13,21 @@
 
 class ArraySystemProperties implements SystemPropertiesInterface
 {
+    /**
+     * Data supplied to the constructor. We need to save this shortly to avoid
+     * code warnings.
+     */
+    private $data;
+
     /**
      * {@inheritdoc}
      */
     public function __construct(array $data)
     {
-        // Little "hack" to trick PHPStan
-        // Not the cleanest thing, but it works.
-        $data;
+        // this avoids the unused warning
+        $this->data = $data;
+        // this avoids using more RAM than necassary :)
+        $this->data = null;
     }
 
     /**