Summary:Removed eslint rule that checks modules

After we updated to ESLint 2.x, ESLint started complaining `'use strict' is unnecessary inside of modules  strict`.
This is correct behaviour because according to spec modules are strict.
The problem is that our transforms don't transpile strict mode so we still need to have this pragma in all our code.

I did not find a way to make eslint require "use strict" for ES6 modules: https://github.com/eslint/eslint/issues/2785
So I am removing this.

What stops us from automatically adding strict mode with babel?

Need your feedback, frantic martinbigio
David said that you Martin looked into this.
Closes https://github.com/facebook/react-native/pull/6403

Differential Revision: D3038039

Pulled By: martinbigio

fb-gh-sync-id: b8a00c093768a318487dcb89e433859825a08b2c
shipit-source-id: b8a00c093768a318487dcb89e433859825a08b2c