Remove pointless Message::toJson()

Author: clue

example/events.php

@@ -25,7 +25,7 @@ function (Client $client) use ($loop) {
         });
 
         $client->on('event', function (Event $event) {
-            echo 'Event: ' . $event->getName() . ': ' . $event->toJson() . PHP_EOL;
+            echo 'Event: ' . $event->getName() . ': ' . json_encode($event->getFields()) . PHP_EOL;
         });
     },
     function (Exception $error) {

src/Protocol/Message.php

@@ -24,11 +24,6 @@ public function getField($key)
         return null;
     }
 
-    public function toJson()
-    {
-        return json_encode($this->getFields());
-    }
-
     public function getFields()
     {
         return $this->fields;