Delete Webxdc infomessages when webxdc is deleted

[link2xt]

When Webxdc instance is deleted, info messages pointing to it currently remain in the chat. They however cannot be used to jump to the message anymore, so they are not useful. If user deletes the instance or the instance is deleted remotely ("delete for everyone"), related info messages should be deleted as well.

Reported by @adbenitez in some chat.

[adbenitez]

besides just not being useful there are actual problems: they have different IDs per device so deleting in one device doesn't delete for everyone nor even for your oder devices, so you have to delete several info message manually from every device