Revert "fix: don't modify ssh_config for ubuntu-cpc projects (LP:1968873)"

This change triggered a bug in cloud-init (see LP:1968873). cloud-init
does not recongnize sshd options set in /etc/ssh/sshd_config.d/ and
cloud-init modifies directly /etc/ssh/sshd_config which gets then
overwritten by settings from /etc/ssh/sshd_config.d/ .

This reverts commit b54d24ff33.

live-build/ubuntu-cpc/hooks.d/chroot/052-ssh_authentication.chroot

@@ -1,5 +1,3 @@
 #!/bin/bash
 
-cat << EOF >> "/etc/ssh/sshd_config.d/10-cloudimg-settings.conf"
+sed -i "s|#PasswordAuthentication yes|PasswordAuthentication no|g" /etc/ssh/sshd_config
-PasswordAuthentication no
-EOF