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/client/async-ssl-system-executor/websocket_client_async_ssl_system_executor.cpp

@@ -16,13 +16,12 @@
 #include "example/common/root_certificates.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/ssl.hpp>
 #include <boost/asio/strand.hpp>
 #include <boost/asio/system_executor.hpp>
 #include <cstdlib>
-#include <functional>
 #include <iostream>
 #include <memory>
 #include <string>
@@ -47,8 +46,7 @@ fail(beast::error_code ec, char const* what)
 class session : public std::enable_shared_from_this<session>
 {
     tcp::resolver resolver_;
-    websocket::stream<
-        beast::ssl_stream<beast::tcp_stream>> ws_;
+    websocket::stream<ssl::stream<beast::tcp_stream>> ws_;
     beast::flat_buffer buffer_;
     std::string host_;
     std::string text_;

example/websocket/client/async-ssl/websocket_client_async_ssl.cpp

@@ -16,12 +16,11 @@
 #include "example/common/root_certificates.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/ssl.hpp>
 #include <boost/asio/strand.hpp>
 #include <cstdlib>
-#include <functional>
 #include <iostream>
 #include <memory>
 #include <string>
@@ -46,8 +45,7 @@ fail(beast::error_code ec, char const* what)
 class session : public std::enable_shared_from_this<session>
 {
     tcp::resolver resolver_;
-    websocket::stream<
-        beast::ssl_stream<beast::tcp_stream>> ws_;
+    websocket::stream<ssl::stream<beast::tcp_stream>> ws_;
     beast::flat_buffer buffer_;
     std::string host_;
     std::string text_;

example/websocket/client/coro-ssl/websocket_client_coro_ssl.cpp

@@ -16,10 +16,10 @@
 #include "example/common/root_certificates.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/spawn.hpp>
+#include <boost/asio/ssl.hpp>
 #include <cstdlib>
 #include <functional>
 #include <iostream>
@@ -55,8 +55,7 @@ do_session(
 
     // These objects perform our I/O
     tcp::resolver resolver(ioc);
-    websocket::stream<
-        beast::ssl_stream<beast::tcp_stream>> ws(ioc, ctx);
+    websocket::stream<ssl::stream<beast::tcp_stream>> ws(ioc, ctx);
 
     // Look up the domain name
     auto const results = resolver.async_resolve(host, port, yield[ec]);

example/websocket/client/sync-ssl/websocket_client_sync_ssl.cpp

@@ -16,12 +16,11 @@
 #include "example/common/root_certificates.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/connect.hpp>
 #include <boost/asio/ip/tcp.hpp>
-#include <boost/asio/ssl/stream.hpp>
+#include <boost/asio/ssl.hpp>
 #include <cstdlib>
 #include <iostream>
 #include <string>
@@ -62,13 +61,13 @@ int main(int argc, char** argv)
 
         // These objects perform our I/O
         tcp::resolver resolver{ioc};
-        websocket::stream<beast::ssl_stream<tcp::socket>> ws{ioc, ctx};
+        websocket::stream<ssl::stream<tcp::socket>> ws{ioc, ctx};
 
         // Look up the domain name
         auto const results = resolver.resolve(host, port);
 
         // Make the connection on the IP address we get from a lookup
-        auto ep = net::connect(get_lowest_layer(ws), results);
+        auto ep = net::connect(beast::get_lowest_layer(ws), results);
 
         // Set SNI Hostname (many hosts need this to handshake successfully)
         if(! SSL_set_tlsext_host_name(ws.next_layer().native_handle(), host.c_str()))