docs(emqx_bridge_azure_event_hub): remove timestamp from message template example

apps/emqx_bridge_azure_event_hub/src/emqx_bridge_azure_event_hub.erl

@@ -270,8 +270,7 @@ values(producer) ->
             topic => <<"topic">>,
             message => #{
                 key => <<"${.clientid}">>,
-                value => <<"${.}">>,
-                timestamp => <<"${.timestamp}">>
+                value => <<"${.}">>
             },
             max_batch_bytes => <<"896KB">>,
             partition_strategy => <<"random">>,