Remove .polyfill() api. about smoothscroll

[DanielHeath]

It provides a hook for things like rewire and makes it easier to manage when doing e.g. universal server rendering.

[jeremenichelli]

@DylanPiercey this not an issue indeed but more of a decision to follow the pattern used in other polyfills. in this case, the best way is to provide to developer to implicitly apply the polyfill, as @DanielHeath mentioned, to avoid errors in certain cases.

[coladict]

I think this explanation should be added to the Readme.md

import smoothscroll from 'smoothscroll-polyfill';
smoothscroll.polyfill(); // call when initializing web-page or it won't work

Because as someone not familiar to the disaster that is the JS eco-system, I would never know that the given example require('smoothscroll-polyfill').polyfill(); translates to that.