Update new-deprecations.md

Author: laoneo

migrations/44-50/new-deprecations.md

@@ -16,3 +16,8 @@ This page is unfinished, please use the **Edit this Page** link at the bottom of
 
 File: libraries/src/Application/WebApplication.php
 Replacement: The $item_associations property will be removed with no replacement as it is not used in core anymore.
+
+#### Privacy plugin app property is deprecated
+
+File: administrator/components/com_privacy/src/Plugin/PrivacyPlugin.php
+Replacement: The `$this->app` property is deprecated in the privacy plugins. Instead of use `$this->getApplication()` when the plugin is converted to service providers.