Function deltachat::imex::adjust_delete_server_after

async fn adjust_delete_server_after(context: &Context) -> Result<()>

Sets Config::DeleteServerAfter to “never” if needed so that new messages are present on the server after a backup restoration or available for all devices in multi-device case. NB: Calling this after a backup import isn’t reliable as we can crash in between, but this is a problem only for old backups, new backups already have DeleteServerAfter set if necessary.