fix message embed json serialization (#2420)

* fix message embed json serialization

remove the toJSON method on message embeds so the raw data is exposed
for JSON seralization. this removes the hexColor property, but it
probably should not have been there in the first place. fixes #2419

* change api transform to tojson

src/structures/MessageEmbed.js

@@ -302,16 +302,11 @@ class MessageEmbed {
     return this;
   }
 
-  toJSON() {
-    return Util.flatten(this, { hexColor: true });
-  }
-
   /**
    * Transforms the embed object to be processed.
    * @returns {Object} The raw data of this embed
-   * @private
    */
-  _apiTransform() {
+  toJSON() {
     return {
       title: this.title,
       type: 'rich',