Kill es5 shim/sham. Arise, es6 shim.

- [x] @Aintaer 
- [ ] @mikesherov 

Hard to see but `function.prototype.bind` was kept: https://github.com/behance/assets-vendor/pull/10/files#diff-3a6bf705b1ed1ca1478c414e543b26e6R36
revert this cosmetic change.