Clean up examples

[nicolaskruchten]

We have https://github.com/plotly/react-plotly.js/tree/master/example and https://github.com/plotly/react-plotly.js/tree/master/docs/example and https://github.com/plotly/react-plotly.js-demo-app ... Probably we only need 1 or 2 of those, not all 3!