Issue #2350835 by pwolanin: Mark EntityInterface::getSystemPath() as deprecated.

core/lib/Drupal/Core/Entity/EntityInterface.php

@@ -171,6 +171,9 @@ public function link($text = NULL, $rel = 'canonical', array $options = []);
    *
    * @return string
    *   The internal path for this entity.
+   *
+   * @deprecated in Drupal 8.x-dev, will be removed before Drupal 8.0.0. Use
+   *    static::urlInfo() instead.
    */
   public function getSystemPath($rel = 'canonical');