Remove "back to top" link in the footer

Over the month of July:
- Page views: 85,707,043
- Clicks on "Back to top": 34,000 (0.04%)

## Before

![screen shot 2013-08-01 at 16 31 35](https://f.cloud.github.com/assets/85783/894800/8fec574c-fabf-11e2-93c6-626f4d70fd43.PNG)

## After

![screen shot 2013-08-01 at 16 31 53](https://f.cloud.github.com/assets/85783/894802/93c34c5e-fabf-11e2-820e-cbfed13c2652.PNG)


![Grenade!](http://gifs.gifbin.com/012012/1326738234_grenade_drill_fail.gif)