Removed broken fallback. Fixes #152

With Twitch's UI change of today, the Viewers List button is now an `a.button > svg.svg-viewers` and no longer matches `buttons.viewers` which triggers the load of a fallback script. It appears like that fallback script URL was never working in the first place, and thus nothing is loaded and everything breaks.

The script actually *works fine* with the new UI, there's no need for a fallback. Therefore, I suggest we simply remove the fallback and bring it back later if needed (preferably *with* an actual fallback script on the `gh-pages`).