MEDIUM: stream: do not forcefully close the client connection anymore

Now that the mux will take care of closing the client connection at the
right moment, we don't need to close the client connection anymore, and
we just need to close the conn_stream.
diff --git a/src/stream.c b/src/stream.c
index d347f47..5a5adb7 100644
--- a/src/stream.c
+++ b/src/stream.c
@@ -296,7 +296,6 @@
 	struct proxy *fe = sess->fe;
 	struct bref *bref, *back;
 	struct conn_stream *cli_cs = objt_cs(s->si[0].end);
-	struct connection *cli_conn = cs_conn(cli_cs);
 	int i;
 
 	if (s->pend_pos)
@@ -344,11 +343,8 @@
 		http_end_txn(s);
 
 	/* ensure the client-side transport layer is destroyed */
-	/* XXX cognet: wrong for multiple streams in one connection */
-	if (cli_conn) {
-		conn_stop_tracking(cli_conn);
-		conn_full_close(cli_conn);
-	}
+	if (cli_cs)
+		cs_close(cli_cs);
 
 	for (i = 0; i < s->store_count; i++) {
 		if (!s->store[i].ts)