Remove esprima-fb and use Syntax from jstransform

Since https://github.com/facebook/jstransform/pull/29 was merged, `esprima-fb` is not necessary.

The changes to `jstransform` (https://github.com/facebook/jstransform/compare/f59f2e3...13e63c1) include getter/setters for `Class` by passing `{es5:true}` in `options` to `transform`. @zpao any thoughts on whether I should include the option in `bin/jsx` and/or have it as default in `main.js`?