fix: Correctly delete unneeded messages on the server; Remove "Delete Messages from Server" (delete_server_after) config option (#8240)

Fix https://github.com/chatmail/core/issues/8195
Supersedes https://github.com/chatmail/core/pull/8217

The most interesting change is in `delete_expired_imap_messages()`
because there, messages are marked for deletion on single-device
chatmail profiles.

The logic in `delete_expired_imap_messages()` was wrong before, and
pre-messages were not deleted at all. This is fixed by also querying
`pre_rfc724_mid` in addition to `rfc724_mid` from the `msgs` table.
In order not to make the SQL statement too complex, I split it into two.

WRT tests:
- `test_immediate_autodelete()` tests the auto-deletion;
`test_imap_autodelete_fully_downloaded_msg()` tests that even for a
message that is split into pre- and post-message, both messages are
deleted.
- A lot of tests test that if bcc_self is on, messages are not
auto-deleted. E.g. `test_one_account_send_bcc_setting()` and
`test_markseen_message_and_mdn()` relies on the fact that messages stay
on the server when bcc_self is on.
- Unfortunately, it is not possible to test that messages are only
deleted for chatmail servers, because we don't have any tests that use a
non-chatmail server.

src/receive_imf.rs

@@ -910,10 +910,8 @@ UPDATE config SET value=? WHERE keyname='configured_addr' AND value!=?1
     }
 
     // Get user-configured server deletion
-    let delete_server_after = context.get_config_delete_server_after().await?;
-
     if !received_msg.msg_ids.is_empty() {
-        let target = if received_msg.needs_delete_job || delete_server_after == Some(0) {
+        let target = if received_msg.needs_delete_job {
             Some("".to_string())
         } else {
             None