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/mux_h2.c b/src/mux_h2.c
index cfffd69..c405ea6 100644
--- a/src/mux_h2.c
+++ b/src/mux_h2.c
@@ -15,7 +15,6 @@
 #include <haproxy/api.h>
 #include <haproxy/cfgparse.h>
 #include <haproxy/connection.h>
-#include <haproxy/conn_stream.h>
 #include <haproxy/dynbuf.h>
 #include <haproxy/h2.h>
 #include <haproxy/hpack-dec.h>
@@ -28,6 +27,7 @@
 #include <haproxy/net_helper.h>
 #include <haproxy/session-t.h>
 #include <haproxy/stats.h>
+#include <haproxy/stconn.h>
 #include <haproxy/stream.h>
 #include <haproxy/trace.h>