Make mobx-react-lite sideEffect free

[romulof]

Hi,

I just noticed that my bundler is not tree shaking mobx-react-lite, due to it not having "sideEffects": false in its package.json.

I also noticed it was reverted because of this reported bug: #2689

The real issue is assertEnvironment module. It has sideEffects, but it could be replaced with checks inside the function calls fenced with if ("production" !== process.env.NODE_ENV) { /* check */ }, so bundlers and minifiers can strip it from production code.

This way errors could be caught by React error boundaries, which could prevent a full application break and indicate which part of the application was the culprit.