Remove "hacking" section from CONTRIBUTING.md (#6478)
Remove "hacking" section from CONTRIBUTING.md (#6478)

Removes outdated "hacking" section. Fixes #6460.
reactjs/react-router,rackt/react-router,ReactTraining/react-router,ReactTraining/react-router,ReactTraining/react-router,rackt/react-router,ReactTraining/react-router,reactjs/react-router