Remove `speechinput` test

`x-webkit-speech` is already [disabled in the last Chrome Canary](http://jsbin.com/hocetoha/1):

![screen shot 2014-05-02 at 00 29 17](https://cloud.githubusercontent.com/assets/1223565/2857506/aee28820-d178-11e3-8571-2cc253668f3a.png)

and it will soon be completely remove from from Chrome:

* https://code.google.com/p/chromium/issues/detail?id=223198
* https://code.google.com/p/chromium/issues/detail?id=360448