meta-lxatac-bsp: ssh: drop remaining custom config

[hnez]

As of langdale Include /etc/ssh/sshd_config.d/*.conf is part of the default sshd_config, which means we can deploy custom config via drop-in files.

This change prompted me to have a look which config options should go into such a drop in file.

A diff between:

$ sort meta-lxatac-bsp/recipes-core/openssh/openssh/sshd_config | \
  grep -v "^#" > upstream
$ sort ./poky/meta/recipes-connectivity/openssh/openssh/sshd_config | \
  grep -v "^#" > ours

yields:

25a26
> ChallengeResponseAuthentication no
29,30c30,33
< Include /etc/ssh/sshd_config.d/*.conf
< KbdInteractiveAuthentication no
---
> Include sshd_config.d/*.conf
> PasswordAuthentication no
> PermitRootLogin yes
> PubkeyAuthentication yes

Which breaks down to:

• ChallengeResponseAuthentication is an alias for KbdInteractiveAuthentication -> equivalent result
• The Include states are also equivalent
• PubkeyAuthentication yes is the default -> no effect
• The default for PermitRootLogin is prohibit-password, which means password based login is disabled for root. As we only have a root user this means the behavior of the default config is again equivalent with our config.

Drop the custom config for easier maintainance.