Remove hard-coded max-width from markdown pages

[evwilkin]

Our website docs have an arbitrary max-width applied to a wrapper element that content loads within in mdx.js which does not always work well for all content such as large tables and causes hacky workarounds.

We should look at either removing this max-width and confirm a new design direction for laying out content on the page, or at least move this rule down so that each page can more easily override the value individually where needed.