Update lib/private/Security/Certificate.php

Co-authored-by: Côme Chilliet <91878298+come-nc@users.noreply.github.com>
Signed-off-by: Faraz Samapoor <f.samapoor@gmail.com>

lib/private/Security/Certificate.php

@@ -36,7 +36,6 @@ class Certificate implements ICertificate {
 
 	protected ?string $organization;
 
-	protected $serial;
 
 	protected \DateTime $issueDate;