Don't artificially limit the width of the docs

[pde]

The table here:

https://certbot.eff.org/docs/using.html#plugins

renders too narrowly on wide screens. That's because of an 800px max-width CSS attribute; not sure that it needs to be there!

[pde]

It's in .wy-nav-content

[bmw]

Some progress on this was made in https://github.com/certbot/website/pull/275 but got some pushback from E&D.

I'm going to close the PR but leave this issue open so hopefully someone can look at it in the future and take from that PR if they wish.