Unnecessary scrollbar in sidebar

[rvighne]

When the screen is large enough that there's enough space for all the items in the sidebar, it still displays a scrollbar. It's disabled, so it isn't useful and looks out-of-place:

This was introduced by #378, specifically this section of screen.scss, which forces scrolling:

  @media #{$large-screen} {
    overflow-y: scroll;
  }

But simply removing that line causes a regression in the bug it was originally trying to fix, so I'm not sure what's the best way to address this.