Remove login requirement for gifting osu!supporter

[PashaSudak]

Simplify gifting process for non osu! players that doesnt have an account by removing login requirement to gift people osu!supporter.

Easier to get gifts from family/friends etc.

[Joehuu]

Probably makes sense for the physical merch too.

[peppy]

If it can happen I'm not against it, but it sounds like quite a bit of work.

But do keep in mind that we previously disabled purchases from restricted users due to fraud. This would open that door back up.