horror_(theme) -> horror

BUR #7334 has been rejected.

create alias horror_(theme) -> horror

The qualifier on the tag horror_(theme) is a relic from when horrified was called horror_(expression). It's no longer necessary to make the distinction, especially since the horror_(expression) → horrified alias is displayed as soon as you type in the characters "horr" anyway.

Outside of danbooru "horror" means both things, which is why it's qualified. There's still a pretty high chance someone unfamiliar with the site's tags could confuse them.

The bulk update request #7334 (forum #197303) has been rejected by @nonamethanks.