Remove functions that can be polyfilled now

[moonglum]

Due to some new functions on Node, you could remove some of the DOM utilities from this lib, asking users to replace them with polyfills of the Node functions. You can find out more about these in this article:

• replaceNode can be replaced with replaceWith ⚠️ This is experimental, maybe we should wait?
• prependChild can be replaced with prepend ⚠️ This is experimental, maybe we should wait?
• removeNode can be replaced with remove

[moonglum]

There is also a good polyfill now: https://github.com/WebReflection/dom4