dillon1000/react

Tweak syntax in rollup build script (#9852)

* Tweak syntax in rollup build script

@bvaughn and I already discussed this.

**test plan:**
`yarn build`

* Remove JSDoc comments

**what is the change?:**
removing some comments

**why make this change?:**
The code is basically self explanatory and these comments could get out
of sync.

**test plan:**
Visual inspection, `yarn build` and `yarn test`

**issue:**
https://github.com/facebook/react/issues/9398