[APPROVED] dennou_shoujo_youtuber_shiro --> siro

BUR #2206 has been approved by @evazion.

create alias dennou_shoujo_youtuber_shiro -> dennou_shoujo_youtuber_siro
create alias shiro_(dennou_shoujo_youtuber_shiro) -> siro_(dennou_shoujo_youtuber_siro)

Reason: Official spelling. I've seen commenters on Danbooru use the Siro spelling, so I guess people are fine with it.

EDIT: The bulk update request #2206 (forum #161586) has been approved by @evazion.

This and topic #16483 looks like one of those cases where we don't use the official romanization because it goes against our romanization guidelines. In this case, シロ -> shiro. Personally I don't like going against official spellings even if they are "wrong" by our standards, but that's what our policy is.

We've done some exceptions in the past on copyright tags when there is an official name so I don't see why we can't do the same in this case. Also, the rules are very old now.

The bulk update request #2206 (forum #161586) has been approved by @evazion.