Fix PHPStan errors

src/StaticPHP/Util/FileSystem.php

@@ -370,17 +370,6 @@ class FileSystem
         self::createDir($dir_name);
     }
 
-    /**
-     * Add source extraction hook
-     *
-     * @param string   $name     Source name
-     * @param callable $callback Callback function
-     */
-    public static function addSourceExtractHook(string $name, callable $callback): void
-    {
-        self::$_extract_hook[$name][] = $callback;
-    }
-
     /**
      * Check if path is relative
      *