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.

deltachat-rpc-client/tests/test_something.py

@@ -1240,10 +1240,12 @@ def test_leave_and_delete_group(acfactory, log):
 
 
 def test_immediate_autodelete(acfactory, direct_imap, log):
+    """
+    `bcc_self` is off by default,
+    so that messages are supposed to be immediately autodeleted
+    """
     ac1, ac2 = acfactory.get_online_accounts(2)
-
-    # "1" means delete immediately, while "0" means do not delete
-    ac2.set_config("delete_server_after", "1")
+    assert ac1.get_config("bcc_self") == "0"
 
     log.section("ac1: create chat with ac2")
     chat1 = ac1.create_chat(ac2)