Remove the amss field from tcpip.tcp.handshake as it was unused

The amss field in the tcpip.tcp.handshake was not used anywhere. Removed it to
not cause confusion with the amss field in the tcpip.tcp.endpoint struct, which
was documented to be used (and is actually being used) for the same purpose.

PiperOrigin-RevId: 276577088

tcpip/transport/tcp/connect.go

diff --git a/tcpip/transport/tcp/connect.go b/tcpip/transport/tcp/connect.go
index 1933f75..ee113a4 100644
--- a/tcpip/transport/tcp/connect.go
+++ b/tcpip/transport/tcp/connect.go
@@ -78,9 +78,6 @@
 	// mss is the maximum segment size received from the peer.
 	mss uint16
 
-	// amss is the maximum segment size advertised by us to the peer.
-	amss uint16
-
 	// sndWndScale is the send window scale, as defined in RFC 1323. A
 	// negative value means no scaling is supported by the peer.
 	sndWndScale int