Simplify bin/jsx to perform just the JSX transform

We will continue using `bin/jsx-internal`, well, internally.

Note that this version no longer respects `@providesModule`, and it doesn't do anything special with constants like `__DEV__`, so we can no longer get to claim that `bin/jsx` can be used to build the core.

I'm happy about this, personally, because it demonstrates the flexibility of Commoner.

cc @zpao @petehunt