fix: Delete resent messages on receiver side (#5155)

If a Delta Chat message has the Message-ID already existing in the db, but a greater "Date", it's a
resent message that can be deleted. Messages having the same "Date" mustn't be deleted because they
can be already seen messages moved back to INBOX. Also don't delete messages having lesser "Date" to
avoid deleting both messages in a multi-device setting.

python/tests/test_1_online.py

@@ -543,6 +543,27 @@ def test_forward_own_message(acfactory, lp):
     assert msg_in.is_forwarded()
 
 
+def test_resend_message(acfactory, lp):
+    ac1, ac2 = acfactory.get_online_accounts(2)
+    chat1 = ac1.create_chat(ac2)
+
+    lp.sec("ac1: send message to ac2")
+    chat1.send_text("message")
+
+    lp.sec("ac2: receive message")
+    msg_in = ac2._evtracker.wait_next_incoming_message()
+    assert msg_in.text == "message"
+    chat2 = msg_in.chat
+    chat2_msg_cnt = len(chat2.get_messages())
+
+    lp.sec("ac1: resend message")
+    ac1.resend_messages([msg_in])
+
+    lp.sec("ac2: check that message is deleted")
+    ac2._evtracker.get_matching("DC_EVENT_IMAP_MESSAGE_DELETED")
+    assert len(chat2.get_messages()) == chat2_msg_cnt
+
+
 def test_long_group_name(acfactory, lp):
     """See bug https://github.com/deltachat/deltachat-core-rust/issues/3650 "Space added before long
     group names after MIME serialization/deserialization".