Remove `text-shadow: none;` from ::selection

No issue

Fixes a weird issue where text would overlap other text.

> @PaulAdamDavis Yea it’s an OpenType / selection bug. You can only change background-color in ::selection with font-feature-settings enabled.

From [@designbyjake](https://twitter.com/designbyjake/status/510772571886075904)

![selection](https://cloud.githubusercontent.com/assets/390392/4260750/19416000-3b4c-11e4-9e3c-cd34d82a01c2.gif)