Twenty Fourteen: Revert Video Header Implementation

[davidakennedy]

For 4.7, Twenty Fourteen got video headers because it made sense to test out implementation in another, existing theme, besides Twenty Seventeen. However, I don't think think the theme should ship with video headers because:

• the theme was never designed with the feature in mind.
• the theme has been around for awhile, and the feature could interfere with existing customizations by users.
• it's okay to have a new feature just be in the latest default theme.

A clean revert can't be done because the changes to the theme were made along with the initial commit for video headers.

See #38172.
See r38985.

[davidakennedy]

Removes video headers for Twenty Fourteen.

[joemcgill]

Not opposed. If we don't revert, we at least need to go back and update the implementation to come back in line with the changes that have been made since.

[karmatosed]

In 39226:

Twenty Fourteen: Removes video header support

Support was added to test implementation but never completed. This removes the test implementation.

Props davidakennedy
Fixes #38783

[celloexpressions]

I'm not necessarily opposed either, but I wouldn't call the implementation incomplete. It worked fully in my testing, and no bugs were reported. That may have changed with later adjustments.

the theme has been around for awhile, and the feature could interfere with existing customizations by users.

I don't think there would be any issues with this, as existing header images are still used in the same way, so the only changes would happen after adding a video.