Revert "ssh: add support for banners"

This reverts commit ed5229da99.

Reason for revert: missing language tag in banner message breaks auth against other implementations.

Change-Id: I18ac5b3fe3b4693688b82ff4b0db02dab739c45b
Reviewed-on: https://go-review.googlesource.com/72381
Reviewed-by: Han-Wen Nienhuys <hanwen@google.com>
Run-TryBot: Han-Wen Nienhuys <hanwen@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>

ssh/handshake.go

@@ -78,11 +78,6 @@ type handshakeTransport struct {
 	dialAddress     string
 	remoteAddr      net.Addr
 
-	// bannerCallback is non-empty if we are the client and it has been set in
-	// ClientConfig. In that case it is called during the user authentication
-	// dance to handle a custom server's message.
-	bannerCallback BannerCallback
-
 	// Algorithms agreed in the last key exchange.
 	algorithms *algorithms
 
@@ -125,7 +120,6 @@ func newClientTransport(conn keyingTransport, clientVersion, serverVersion []byt
 	t.dialAddress = dialAddr
 	t.remoteAddr = addr
 	t.hostKeyCallback = config.HostKeyCallback
-	t.bannerCallback = config.BannerCallback
 	if config.HostKeyAlgorithms != nil {
 		t.hostKeyAlgorithms = config.HostKeyAlgorithms
 	} else {