There is a table with site-to-site entries in MM2 which is not used at all any more.
The only 'benefit' it has right now, is that some sites cannot be deleted from the database as they are listed in the site-to-site table. Especially old mirrors have entries in that table. Just like private inter-mirror-sync URLs this is a concept which is not used/followed in MM2 at all. The table as well as all code around it could be removed.
There is a table with site-to-site entries in MM2 which is not used at all any more.
The only 'benefit' it has right now, is that some sites cannot be deleted from the database as they are listed in the site-to-site table. Especially old mirrors have entries in that table. Just like private inter-mirror-sync URLs this is a concept which is not used/followed in MM2 at all. The table as well as all code around it could be removed.