build: switch to typescript's es2015 typings (#28134)

Note that this allows Angular to depend on the entirety of the ES2015 API, not just our restricted subset.
This change is needed because our copy of the subset was out-of-date, and prevents us using ES2015 target in dev mode.

This is a subset of https://github.com/angular/angular/pull/27738

PR Close #28134

modules/types.d.ts

@@ -13,5 +13,5 @@
 /// <reference types="jasminewd2" />
 /// <reference types="node" />
 /// <reference types="zone.js" />
-/// <reference path="./es6-subset.d.ts" />
+/// <reference lib="es2015" />
 /// <reference path="./system.d.ts" />