sshd_config protocol 1 support completely removed resulting in protocol option being removed

[AngeloThys]

The protocol option has been removed, as openssh now only supports and uses protocol 2.

Therefor we should remove the protocol 2 key-value pair from sshd_config

Source: openssh, release 7.6

ssh(1): delete SSH protocol version 1 support, associated
configuration options and documentation.