remove display: none check, as it's causing rules to be erroneously excluded

[Scott Jehl]

The following condition is causing critical css rules to be excluded even when they are not display none (in some cases, display: table elements weren't making the cut). We should remove this condition until we can pull it off in a way that doesn't have unexpected side effects.

https://github.com/filamentgroup/criticalCSS/blob/master/lib/criticalrunner.js#L116