Revert "Stabilise WebViewTest.testSetDownloadListener"

This reverts commit 323db78c.

    Stabilise WebViewTest.testSetDownloadListener

    Work around a bug in Blink/chromium compositor by posting the navigation
    to the download URL in a setTimeout.

The issue is not reproducible in chromium trunk and added a fix that would
have made the test pass in kkmr2 already.

BUG: 13693414