Remove `speechinput` test

`x-webkit-speech` is already disabled in the last Chrome Canary,
and it will soon be completely removed from from Chrome.

Ref: https://code.google.com/p/chromium/issues/detail?id=223198
     https://code.google.com/p/chromium/issues/detail?id=360448
Merge pull request #1326 from alrra/remove-speechinput-test

Remove `speechinput` test