ui: pbs paperkey: cleanup iframe for printing after window close

Reported-by: Aaron Lauterer <a.lauterer@proxmox.com>
Signed-off-by: Thomas Lamprecht <t.lamprecht@proxmox.com>

www/manager6/storage/PBSEdit.js

@@ -181,6 +181,7 @@ ${prettifiedKey}
 
 	printFrame.src = "data:text/html;base64," + btoa(html);
 	document.body.appendChild(printFrame);
+	me.on('destroy', () => document.body.removeChild(printFrame));
     },
 });