ssh: deprecate DSA keys as per OpenSSH recommendation

Also see: http://www.openssh.com/txt/release-7.0

(cherry picked from commit 4870ff10)

src/etc/rc.sshd

@@ -62,7 +62,6 @@ if (file_exists('/conf/sshd/ssh_host_rsa_key') && !file_exists("{$etc_ssh}/ssh_h
 $keys = array(
 	/* .pub files are implied */
 	'rsa' => 'ssh_host_rsa_key',
-	'dsa' => 'ssh_host_dsa_key',
 	'ecdsa' => 'ssh_host_ecdsa_key',
 	'ed25519' => 'ssh_host_ed25519_key',
 );