Remove unused variable initialisation

Author: pabzm

program/lib/Roundcube/rcube_message.php

@@ -75,9 +75,6 @@ class rcube_message
     /** @var array<rcube_message_part> */
     public $mime_parts = [];
 
-    /** @var array<rcube_message_part> */
-    public $inline_parts = [];
-
     /** @var array<rcube_message_part> */
     public $attachments = [];