Deprecate cover_image

BUR #18312 has been rejected.

deprecate cover_image

Looks like cover image was created before textless version and had a different meaning at first. If it's supposed to be the same as the two tag search textless_version cover_page (not really populated), is it a necessary tag? Is there any other use for it that's not explicit in the wikis?

This bulk update request is pending automatic rejection in 5 days.

If textless_version cover_page is the alternative, I'd prefer if it was more populated, otherwise it's not really an alternative as it currently stands.

This bulk update request has been rejected because it was not approved within 45 days.

The bulk update request #18312 (forum #247669) has been rejected by @DanbooruBot.