Unpublish media entity URL when the media entity is deleted.

This should be similar to file deletion but have to deal with all core media types except Remote Video:

• Audio
• Document
• Image
• Video

Fix is here:

https://github.com/quantcdn/drupal/pull/236

but does not handle image styles. That's been pulled out into its own issue:

📌 Unpublish image style URLs when the image or media entity is deleted. Active

Merged into 8.x-1.x and 2.x