Receiving of re-sent deleted messages (#7115)

[iequidoo]

Helps #7115. Not sure about the second commit because it breaks the scenario described in ephemeral.rs:

//! When Delta Chat deletes the message locally, it moves the message
//! to the trash chat and removes actual message contents. Messages in
//! the trash chat are called "tombstones" and track the Message-ID to
//! prevent accidental redownloading of the message from the server,
//! e.g. in case of UID validity change.

But the first one shouldn't make harm even for Gmail (tested it with my account with "Watch Sent Folder" set) which copies sent messages to Sent because if the user deletes the message, either it has already appeared on both mailboxes or hasn't really sent yet, i.e. it's quite hard to catch a race and see that the message reappears after deletion, at least i haven't succeeded with this.