Remove support for pre-authentication compression. Doing compression
early in the protocol probably seemed reasonable in the 1990s, but
today it's clearly a bad idea in terms of both cryptography (cf.
multiple compression oracle attacks in TLS) and attack surface.

Moreover, to support it across privilege-separation zlib needed
the assistance of a complex shared-memory manager that made the
required attack surface considerably larger.

Prompted by Guido Vranken pointing out a compiler-elided security
check in the shared memory manager found by Stack
(http://css.csail.mit.edu/stack/); ok deraadt@ markus@

NB. pre-auth authentication has been disabled by default in sshd
for >10 years.
input_userauth_banner(int type, u_int32_t seq, void *ctxt)
{
	char *msg, *lang;
	u_int len;

	debug3("%s", __func__);
	msg = packet_get_string(&len);
	lang = packet_get_string(NULL);
	if (len > 0 && options.log_level >= SYSLOG_LEVEL_INFO)
		fmprintf(stderr, "%s", msg);
	free(msg);
	free(lang);
	return 0;
}

input_userauth_banner(int type, u_int32_t seq, void *ctxt)
{
	char *msg, *lang;
	u_int len;

	debug3("%s", __func__);
	msg = packet_get_string(&len);
	lang = packet_get_string(NULL);
	if (len > 0 && options.log_level >= SYSLOG_LEVEL_INFO)
		fmprintf(stderr, "%s", msg);
	free(msg);
	free(lang);
	return 0;
}
