Remove custom styles that were adding a scrollbar on wide browsers

The 'margin-right' of the #content was being set to 240px for all media sizes, even though the sidebar is only 240px in the 'medium' size (it's 300px in the large size). This led to a horizontal scrollbar appearing.

I gave the curriculum a once-over after the change and it doesn't look broken to me, but I don't know what these styles were trying to achieve so I can't say for sure. The only visual change I can detect is the addition of a (harmless) blank sidebar to the curriculum index page.

### Before

![hilobefore](https://f.cloud.github.com/assets/1041691/2406853/35e25fcc-aa7c-11e3-89b7-07c2a3d1eb53.png)

### After

![screen shot 2014-03-12 at 11 48 39 pm](https://f.cloud.github.com/assets/1041691/2406854/41527b1c-aa7c-11e3-961d-b4f7ad9a2fae.png)