[Docs] Remove most of @jsx

I kept some places intact (search for @jsx) because they require other bigger changes:

- ref-01-top-level-api.md
- grunt/tasks/npm.js
- old blog posts (don't change those)
- examples/ folder, as they have their own package.json that rely on old dependencies (node-jsx, reactify) that haven't upgraded to 0.12
Merge pull request #2370 from chenglou/rm-school

[Docs] Remove most of @jsx