fix(build): switch to cjs output for es5.

System output does not work at the current versions of TS and
system.js. Will revisit after upgrading TS.

Removes unused traceur tooling.

Closes #3974

modules/benchmarks_external/src/tree/react/react.min.d.ts

@@ -1,2 +1,2 @@
-declare var React: any;
-export default React;
+export var createElement: Function;
+export var render: Function;