Remove unnecessary polyfills

[negezor]

Screenshot

Expected Behaviour
No polyfills

Actual Behaviour
Provided a polyfill for await and iterator, which appeared in 2016 in the vast majority of browsers. And in Node.js from version 7.6.0. This hurts both performance and codebase size.

Further Information
Polyfills should be implemented by the end developer to avoid bloating the codebase.

[enisdenjo]

Related to #551.

Thank you for reporting! There will be a new major release coming soon that will remove some pending deprecations and bump the lowest supported node (which will improve the bundle).