Remove application_static from docs due to Webpacker changes

[justin808]

Per this search:

https://github.com/shakacode/react-webpack-rails-tutorial/search?utf8=%E2%9C%93&q=application_static&type=

This needs cleanup.

[rnice01]

Hey I'd like to help out with this if I could, seems simple enough.

[justin808]

@rnice01 Please start on this! I'll mark this taken by you, but you have only a few days to show progress. Get in touch if you want a Slack invite as well. And we need to update the docs for https://github.com/shakacode/react_on_rails.

[ramrudra]

@justin808 I'll pick this up

[singhvaibhavram]

@justin808 I would like to take this.

[justin808]

@singhvaibhavram Sure. If we can get proper HMR working as well, that would be great.