chore($$raf) Remove support for prefixed requestAnimationFrame

According to [can I use](http://caniuse.com/#feat=requestanimationframe) this would drop support for the following browsers:
* Firefox 22
* Chrome 23
* Safari 6
* iOS 6.1

Note, they don't have data on Blackberry 10.1 (where it's prefixed) and 10.2 (where it's unprefixed).

This is also the same level of support as provided by [jQuery](https://github.com/jquery/jquery/blob/10399ddcf8a239acc27bdec9231b996b178224d3/src/effects.js#L649).