net::ssl::stream is canonical in examples

We no longer need to use beast::ssl_stream to improve write performance, as
Asio now linearizes scatter/gather I/O in ssl::stream:
https://github.com/chriskohlhoff/asio/commit/17637a48ccbfa2f63941d8393a7c8316a8df4a79

example/websocket/server/sync-ssl/websocket_server_sync_ssl.cpp

@@ -16,11 +16,10 @@
 #include "example/common/server_certificate.hpp"
 
 #include <boost/beast/core.hpp>
-#include <boost/beast/ssl.hpp>
 #include <boost/beast/websocket.hpp>
 #include <boost/beast/websocket/ssl.hpp>
 #include <boost/asio/ip/tcp.hpp>
-#include <boost/asio/ssl/stream.hpp>
+#include <boost/asio/ssl.hpp>
 #include <cstdlib>
 #include <functional>
 #include <iostream>
@@ -43,7 +42,7 @@ do_session(tcp::socket socket, ssl::context& ctx)
     try
     {
         // Construct the websocket stream around the socket
-        websocket::stream<beast::ssl_stream<tcp::socket&>> ws{socket, ctx};
+        websocket::stream<ssl::stream<tcp::socket&>> ws{socket, ctx};
 
         // Perform the SSL handshake
         ws.next_layer().handshake(ssl::stream_base::server);