Remove deprecation notice for .on() since its used for promise BC

lib/promise.js

@@ -117,8 +117,6 @@ SequelizePromise.all = function (promises) {
  * @deprecated
  */
 Promise.prototype.on = function(evt, fct) {
-  deprecated('on() is deprecated and will be removed in 2.1, please use promise-style instead or use logging: fn in method options for method sql log');
-
   if (evt === 'success') {
     this.then(fct);
   }