Cookie was only deleted from current path

When deleting a cookie using `->setCookie('cookieName')` code, then only cookie from current path was deleted. This way if cookie was set on `/index.html` page, then it could not be deleted, while being on `/sub-folder/sub-page.html`.

Here I'm also bringing `->reset()` method of Session up to date with other drivers, so now it ONLY deletes all cookies and nothing more. Before it was also erasing browser history, which prevented `->reload()` method from working properly after session reset.

Tests in https://github.com/Behat/Mink/pull/418

P.S.
Luckily (they don't share same interface) there is `getUri` method (that I'm using) in both `Request` classes, which allowed me to create this PR:
* `\Symfony\Component\HttpFoundation\Request` used in `MinkBrowserKitDriver`
* `\Symfony\Component\BrowserKit\Request` used in `MinkGoutteDriver`