Remove Original-Recipient and Final-Recipient fields from MDNs

[link2xt]

There are two commits, first removes Original-Recipient which was used incorrectly. Second removes Final-Recipient, which is formally required by RFC, but was not set correctly too and is not used anyway.
This is part of #8572, i was looking into why mimefactory still needs to know the "primary" address even with #8619

Commit messages copy-pasted below for convenience:

---

According to
https://datatracker.ietf.org/doc/html/rfc8098#section-3.2.3 Original-Recipient field values in MDNs MUST NOT be included if the information about original recipient is not available. Original recipient may be obtained from ORCPT parameter of SMTP envelope or from Original-Recipient header which MTAs are expected to convert Original-Recipient to.

The way we have been using Original-Recipient field is not correct. Technically we should look for Original-Recipient header on the message when downloading it from IMAP
and then copy the value into MDN,
but simply assuming it is never there is more correct than always assuming it is the same as our current address.

I also grepped for Original-Recipient
and removed it together with Reporting-UA from the tests. Orignal-Recipient is now only left in NDN (bounce messages) test data, there it is correct as this field is added by MTAs that have direct access to ORCPT parameter.

---

This Final-Recipient was not set to the correct value anyway.
We could query the database and find out via imap table
which transport we have received the message on,
but it is not worth the effort as the field is not practically used
and cannot be relied on as old versions still send incorrect value.

This removes one call to get_primary_self_addr()
to make it easier to remove the concept of the "primary"
address eventually.