Alias houso to houso_(touhou)

BUR #21826 has been approved by @evazion.

create alias houso -> houso_(touhou)

These tags are both meant to refer to the same character - Ibaraki Kasen's pet tiger. But because they're so infrequent, we've ended up with a double-up.

Updating the houso_(touhou) as the primary brings it in line with Kasen's other pets, such as Kanda (touhou) and Mukou (touhou).

For the record, as far as I can tell, the only person with a similar name in our tags is housou masamune. With that said, if this alias does cause issues in the future, we can always remove it.

I would also add an unalias.

The bulk update request #21826 (forum #262471) has been approved by @evazion.