fix scrollspy by removing content min-height (closes #1462)

The other removal is basically a clean up, since the scroll spy is already handled in the html itself:
https://github.com/stefanpenner/ember-cli/blob/gh-pages/_layouts/default.html#L4
and
https://github.com/stefanpenner/ember-cli/blob/gh-pages/_layouts/post.html#L4