I read that link already. Wonder if that is outdated. I don't see a menu or any other option to delete a contact in FB messenger. I did finally sync on an iPad to reflect my current friend list. However, kind of bizarre that it will only sync on wifi and keeps old info until deleted. This is messenger. It still has old friends in it, waiting for it to sync now on wifi.
My solution was to delete messenger (iPhone). I don't use it. Additionally, I deleted all the messages in messenger on FB. FB said to do a search to delete old contacts, but who wants to do that? Really odd, it said that it is syncing contacts from my phone, which wasn't true since I have cleaned out my contacts extensively and it loaded a bunch of old contacts.