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

...kes video, plays it back, then deletes it in preview mode
I'd rather update this locator, as finding an element by its name seems kind of unreliable.
We can use By.CSS_SELECTOR instead, so the locator would be: (By.CSS_SELECTOR, 'button[data-l10n-id="delete"]')
Can you please update it?