Remove babel-register

[danneu]

I was too eager to test my react-template-render library in koa-skeleton and thus replaced my Pug templates with .jsx templates. But now I need Babel to compile .jsx into .js.

The easiest solution was to use babel-register: https://github.com/danneu/koa-skeleton/blob/30ccf95b1e7f1de245d7252dd4fbf043e0e16616/src/index.js#L4-L7

But it brings a thick runtime dependency, probably slows down large project boot, and probably degrades the quality of stack traces.

Better would be to compile .jsx to .js physically with a watch script.

It's kind of lame to have a build step at all on a server, but so far .jsx templates have been worth it. Prob on par with what I had with Pug.