Drop Normalize.css in v4

Reversing course from #20388 (closed).

I hate doing this right after our last alpha when we should be focused on as few changes as possible, but for stability of the project moving forward, I'm thinking we need to drop Normalize.css from v4. Here's why.

• In their next major release, they plan to remove all opinionated styles. That includes fonts, body's default margin, and more—all of which we rely on.
• The last major release, Normalize 5, removed the font: inherit normalization from common form and button elements, causing #21588 (closed) (and several duplicate issues, sorry!).
• There are a ton of overrides we don't need given our browser support (e.g., IE9-, Safari 6, and iOS 4-7), meaning we can remove some unused code.
• Having our resets split across files really kinda sucks. This will consolidate them into a single point of reference for everyone.

Weigh in below if you have thoughts or feels. I'm drafting up a PR to see what this looks like in practice.