Removed deprecated warning: "Webkit only supports pixels for the start and end stops for radial gradients"

See note at:   https://developer.apple.com/library/safari/documentation/InternetWeb/Conceptual/SafariVisualEffectsProgGuide/Gradients/Gradient.html#//apple_ref/doc/uid/TP40008032-CH10-SW15
```
The -webkit-linear-gradient and webkit-radial-gradient properties require iOS 5.0 or later, or Safari 5.1 or later on the desktop. 
If you need to support earlier releases of iOS or Safari, see “Prior Syntax (-webkit-gradient).”
```

It's not really clear why this warning is there in first place, as even the "Prior Syntax" has an example with start/stop using percentage:   
```
-webkit-gradient(radial, 20% 20%, 0px, 20% 20%, 60px, from(white), to(black))
```