Clean up docs

[hammer]

While working on #504 I noticed a few things that make the docs look cleaner, in my opinion. I'm curious to hear from others.

• Remove Indices and tables section from index.rst. The index takes a while to build and seems primarily useful in a book context. We have a search box, that seems more useful to me.
• Remove the "fullscreen" and "download" links on every page. The browser can handle these functions.
• Remove the table of contents at the top of each page. The theme includes a right sidebar with a table of contents already, no need to duplicate this content and push page content down.

[hammer]

It turns out the right sidebar is not shown on mobile, so the TOC on each page could plausibly stay. I would still recommend we get rid of it, though, as it's quite large and not usually what the user wants.