Splitting asymmetrical horns into separate tags

BUR #18668 has been approved by @nonamethanks.

create implication uneven_horns -> asymmetrical_horns
create implication mismatched_horns -> asymmetrical_horns

We've been doing the same for all the other asymmetrical_* tags serving 2 different purposes asymmetrical legwear, asymmetrical gloves, asymmetrical sleeves, and so on.

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

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

The bulk update request #18668 (forum #249015) has been rejected by @DanbooruBot.

The bulk update request #18668 (forum #249015) has been approved by @nonamethanks.