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.
get_hostkey_private_by_type(int type, int nid, struct ssh *ssh)
{
	return get_hostkey_by_type(type, nid, 1, ssh);
}

get_hostkey_private_by_type(int type, int nid, struct ssh *ssh)
{
	return get_hostkey_by_type(type, nid, 1, ssh);
}
