fix bug: remove mandatory width for images on 1-column pages

Initially, I was trying to automatically set a full-width for images placed on 1-column pages (like this http://www.cms.int/cop11) because the client wanted full-width images on certain pages.

But it's impossible to automatically differentiate between this page http://www.cms.int/en/about/secretariat and this page http://www.cms.int/cop11, although both pages use an 1-column page layout.

So the initial client request (full-width images on certain pages) must be achieved by the client by uploading 1140px width images on pages in which  they want full-width images.