feat: Delete vg-request-with-auth from IMAP after processing (#6208)

In multi-device case `vg-request-with-auth` left on IMAP may result in situation when Bob joins the
group, then leaves it, then second Alice device comes online and processes `vg-request-with-auth`
again and adds Bob back. So we should IMAP-delete `vg-request-with-auth`. Another device will know
the Bob's key from Autocrypt-Gossip. It's not a problem if Alice loses state (restores from an old
backup) or goes offline for long before sending `vg-member-added`, anyway it may not be delivered by
the server, rather Bob should retry sending SecureJoin messages as he is a part which wants to join,
so let's not solve this for now.

deltachat-rpc-client/tests/test_securejoin.py

@@ -73,22 +73,25 @@ def test_qr_securejoin(acfactory, protect, tmp_path):
     qr_code = alice_chat.get_qr_code()
     bob.secure_join(qr_code)
 
-    # Check that at least some of the handshake messages are deleted.
+    # Alice deletes "vg-request".
+    while True:
+        event = alice.wait_for_event()
+        if event["kind"] == "ImapMessageDeleted":
+            break
+    alice.wait_for_securejoin_inviter_success()
+    # Bob deletes "vg-auth-required", Alice deletes "vg-request-with-auth".
     for ac in [alice, bob]:
         while True:
             event = ac.wait_for_event()
             if event["kind"] == "ImapMessageDeleted":
                 break
-
-    alice.wait_for_securejoin_inviter_success()
+    bob.wait_for_securejoin_joiner_success()
 
     # Test that Alice verified Bob's profile.
     alice_contact_bob = alice.get_contact_by_addr(bob.get_config("addr"))
     alice_contact_bob_snapshot = alice_contact_bob.get_snapshot()
     assert alice_contact_bob_snapshot.is_verified
 
-    bob.wait_for_securejoin_joiner_success()
-
     snapshot = bob.get_message_by_id(bob.wait_for_incoming_msg_event().msg_id).get_snapshot()
     assert snapshot.text == "Member Me ({}) added by {}.".format(bob.get_config("addr"), alice.get_config("addr"))
     assert snapshot.chat.get_basic_snapshot().is_protected == protect