Bug 1100390: Create a new test case for the deletion of video from Preview

Squashed commit from original 1100390 pull request
smoketest = false is set by [default][link], so you can remove it from here.
[link]:https://github.com/mozilla-b2g/gaia/blob/master/tests/python/gaia-ui-tests/gaiatest/tests/manifest.ini#L45