chore(listeners): delete the port override by the env

priv/emqx.schema

@@ -1194,11 +1194,6 @@ end}.
   {datatype, [integer, ip]}
 ]}.
 
-{mapping, "listener.tcp.external", "emqx.listeners", [
-  {datatype, [integer, ip]},
-  {override_env, "TCP_PORT"}
-]}.
-
 {mapping, "listener.tcp.$name.acceptors", "emqx.listeners", [
   {default, 8},
   {datatype, integer}
@@ -1306,11 +1301,6 @@ end}.
   {datatype, [integer, ip]}
 ]}.
 
-{mapping, "listener.ssl.external", "emqx.listeners", [
-  {datatype, [integer, ip]},
-  {override_env, "SSL_PORT"}
-]}.
-
 {mapping, "listener.ssl.$name.acceptors", "emqx.listeners", [
   {default, 8},
   {datatype, integer}
@@ -1479,11 +1469,6 @@ end}.
   {datatype, [integer, ip]}
 ]}.
 
-{mapping, "listener.ws.external", "emqx.listeners", [
-  {datatype, [integer, ip]},
-  {override_env, "WS_PORT"}
-]}.
-
 {mapping, "listener.ws.$name.mqtt_path", "emqx.listeners", [
   {default, "/mqtt"},
   {datatype, string}
@@ -1678,11 +1663,6 @@ end}.
   {datatype, [integer, ip]}
 ]}.
 
-{mapping, "listener.wss.external", "emqx.listeners", [
-  {datatype, [integer, ip]},
-  {override_env, "WSS_PORT"}
-]}.
-
 {mapping, "listener.wss.$name.mqtt_path", "emqx.listeners", [
   {default, "/mqtt"},
   {datatype, string}