cleanup: remove orphan OpenSSH overlay artifacts

Three source-tree leftovers from the OpenSSH-then-Dropbear churn of March
2026 (gretel PR #260 / revert a1e0ad3) that were missed by the earlier
defconfig cleanup in 58fe62f:

1. board/tezuka/common/overlay_base/etc/ssh/sshd_config
   562-byte OpenSSH server config file referenced by nothing on the
   target: no sshd, no openssh-server package, no init script starts it.
   Shipped into /etc/ssh/sshd_config on every boot via the common
   overlay hierarchy, regardless of which defconfig is building, on all
   12 Tezuka boards.

2. board/tezuka/common/overlay_base/etc/init.d/S55hostkeys
   Init script that copies /etc/ssh/ssh_host_* to /mnt/jffs2/etc/ssh/
   for persistence across reboots. No-op without OpenSSH (which
   generates those keys).  Dropbear manages its own host keys under
   /etc/dropbear/ via the `-R` flag passed by S50dropbear.

3. The "Restore OpenSSH host keys from jffs2" block inside S21misc
   (six lines, with a misleading comment). Removed.  The separate
   authorized_keys restore block in the same script is preserved and
   re-commented to clarify it is Dropbear's default pubkey location
   (/root/.ssh/authorized_keys), not OpenSSH-specific.

Net effect on the target rootfs: /etc/ssh/sshd_config no longer ships,
S55hostkeys is gone from /etc/init.d/, and S21misc no longer probes for
non-existent ssh_host_* files.  Dropbear's own host-key lifecycle is
untouched.  User authorized_keys persistence via jffs2 also untouched.

Orphan host-key files left behind in /mnt/jffs2/etc/ssh/ on previously-
deployed targets remain on disk until manually deleted — harmless but
noise.  A follow-up field note may be appropriate for operators who
want to tidy up.

Signed-off-by: Tom Hensel <code@jitter.eu>

Author: gretel

board/tezuka/common/overlay_base/etc/init.d/S21misc

@@ -17,15 +17,10 @@ xo_correction() {
 case "$1" in
 	start|"")
 		printf "Starting miscellaneous setup: "
-		# Restore saved password and SSH keys
+		# Restore saved password database from jffs2
 		[ -d /mnt/jffs2/etc ] && [ -f /mnt/jffs2/etc/passwd ] && [ -f /mnt/jffs2/etc/shadow ] && [ -f /mnt/jffs2/etc/group ] && cd /mnt/jffs2/etc && md5sum -s -c password.md5 && cp passwd shadow group /etc
-		# Restore OpenSSH host keys from jffs2
-		if [ -d /mnt/jffs2/etc/ssh ]; then
-			for key in /mnt/jffs2/etc/ssh/ssh_host_*; do
-				[ -f "$key" ] && cp "$key" /etc/ssh/
-			done
-		fi
-		# Restore authorized_keys
+		# Restore Dropbear authorized_keys from jffs2 (/root/.ssh is the
+		# default path Dropbear uses for user pubkey authorization)
 		[ ! -d /root/.ssh ] && mkdir -p /root/.ssh && chmod 700 /root/.ssh
 		[ -f /mnt/jffs2/etc/ssh/authorized_keys ] && [ ! -f /root/.ssh/authorized_keys ] && cp /mnt/jffs2/etc/ssh/authorized_keys /root/.ssh/authorized_keys && chmod 600 /root/.ssh/authorized_keys