removing comment that mistakes standards compliance for a bug

The following quote from [Selectors Level 3: 5. Groups of Selectors](http://www.w3.org/TR/css3-selectors/#grouping) explains Chrome's behavior:

> **Warning:** the equivalence is true in this example because all the selectors are valid selectors. If just one of these selectors were invalid, the entire group of selectors would be invalid.