[fix] remove brackets around ipv6

rfc/0006_ws2p_v2.md

@@ -279,7 +279,7 @@ The utf8 format is used to display the endpoint in a human-readable format. It i
 
 General utf8 endpoint format :
 
-    API_NAME VERSION n NF1 .. NFn n2 AF1 .. AFn2 IP4 [IP6] HOST PORT PATH
+    API_NAME VERSION n NF1 .. NFn n2 AF1 .. AFn2 IP4 IP6 HOST PORT PATH
 
 NF := NETWORK_FEATURE
 AF := API_FEATURE