REORG: stconn: rename conn_stream.{c,h} to stconn.{c,h}

There's no more reason for keepin the code and definitions in conn_stream,
let's move all that to stconn. The alphabetical ordering of include files
was adjusted.
diff --git a/src/peers.c b/src/peers.c
index 88d609f..b0ed81c 100644
--- a/src/peers.c
+++ b/src/peers.c
@@ -27,7 +27,6 @@
 #include <haproxy/applet.h>
 #include <haproxy/channel.h>
 #include <haproxy/cli.h>
-#include <haproxy/conn_stream.h>
 #include <haproxy/dict.h>
 #include <haproxy/errors.h>
 #include <haproxy/fd.h>
@@ -40,6 +39,7 @@
 #include <haproxy/session-t.h>
 #include <haproxy/signal.h>
 #include <haproxy/stats-t.h>
+#include <haproxy/stconn.h>
 #include <haproxy/stick_table.h>
 #include <haproxy/stream.h>
 #include <haproxy/task.h>