Remove the Masonry lib used in Twenty-Thirteen

It seems an overkill to use this lib for a footer with just a couple of
widgets and it even makes laying them out harder.

Followed the instructions here to deactivate it:
http://slobodanmanic.com/444/flexible-horizontal-sidebars-wordpress-twenty-thirteen-child-theme/
Make the footer's content fit in a width of 750px
Make the top menu fit in 750px