[DOC release] Remove normalizePayload, associated docs, and mention o…

…f functionality.

- Fixes [#3750](#3750)

packages/ember-data/lib/serializers/json-serializer.js

@@ -629,32 +629,6 @@ var JSONSerializer = Serializer.extend({
   },
 
 
-  /**
-    You can use this method to normalize all payloads, regardless of whether they
-    represent single records or an array.
-
-    For example, you might want to remove some extraneous data from the payload:
-
-    ```app/serializers/application.js
-    import DS from 'ember-data';
-
-    export default DS.JSONSerializer.extend({
-      normalizePayload: function(payload) {
-        delete payload.version;
-        delete payload.status;
-        return payload;
-      }
-    });
-    ```
-
-    @method normalizePayload
-    @param {Object} payload
-    @return {Object} the normalized payload
-  */
-  normalizePayload: function(payload) {
-    return payload;
-  },
-
   /**
     @method normalizeAttributes
     @private

packages/ember-data/lib/system/store.js

@@ -1692,9 +1692,6 @@ Store = Service.extend({
 
     Alternatively, `pushPayload` will accept a model type which
     will determine which serializer will process the payload.
-    However, the serializer itself (processing this data via
-    `normalizePayload`) will not know which model it is
-    deserializing.
 
     ```app/serializers/application.js
     import DS from 'ember-data';