Dropping multi-protocol support

[worktycho]

I think we need to keep 1.7 or add support for a testing protocol/framework that works around the encryption in 1.8. I'm currently writing tools that use 1.7 for testing, because the minimal login for 1.7 is two packets. In 1.8 its significantly more complicated.

Also we need to update protoproxy before we can drop 1.7.